UPPER ORDOVICIAN BIVALVES FROM THE OSLO REGION, NORWAY

ROSINE T. TONI

Toni, Rosine T.: Upper Ordovician bivalves from the Oslo Region, Norway. Norsk Geologisk Tidsskrift, Vol. 55, pp. 135-156. Oslo 1975.

This study deals with Upper Ordovician bivalves (Tretaspis series, stages 4c-5b, Upper Caradocian and Ashgillian) of the Oslo Region. Most of the fossils are poorly preserved or incomplete. Twenty-eight species and fifteen genera are identified and compared with previously described species from other regions. The specimens are not systematically collected, but are sampled from different districts.

Rosine T. Toni, Paleontologisk Museum, Sars gt. l. Oslo 5, Norway.

Present address: Department of Geology, Faculty of Science, Alexandria University, Alexandria, Egypt.

The present work is a systematical study of Upper Ordovician bivalves from the Oslo Region, Norway. The material for this study is from collections at Paleontologisk Museum, Oslo (PMO). No new material was collected by me. Previous work has not been done on the Bivalvia of the Upper Ordovi­cian of Norway. H. & T. Soot-Ryen (1960) studied the Middle Ordovician bivalves of the Oslo Region. Only one species - Similodonta spjeldnaesi -

described by these authors was found in the Norwegian Upper Ordovician. The other bivalves are compared with those occurring in the Leptaenakalk in Dalarna, Sweden. They are also related to the North American forms in the Trentonian and Cincinnatian series; and finally to the forms recorded in the Drummuck group, Scotland. The stratigraphical distribution and the Norwegian occurrence of the different species are shown in Table l. The districts from which the fossils were collected are shown on the locality map (Fig. 1).

All the specimens studied were prepared mechanically to free them frpm matrix. Befare photographing, each specimen was coated with dilute black opaque and then by ammonium chloride sublimate. The classification em­ployed herein is that of Moore (ed.) 1969.

Systematic descriptions Family CTENODONTIDAE Worhmann, 1893

Genus Tancrediopsis Beushausen, 1895 Type species. - Ctenodonta contracta Salter, 1859.

Tancrediopsis planodorsata (Ulrich, 1892) Fig, 2, A O Tellinomya planodorsata Ulrich, 1892: 217, fig. 3.

136 R. T. TONI

Distr icts

Oslo- Ask�r

2 Skien- Lc1ng�sund

3 Ring�rike

4 Hc�delclnd

o 'S 10 t'j 20 2'5

Kilom�tr�s !

Fig. l. Districts of the Oslo Region mentioned in the text. (After Henningsmoen 1960).

UP PER ORDOVICIAN BIVALVES FROM OSLO REGION 137

Table 1. Stratigraphical distribution and Norwegian occurrence of Upper Ordovician bivalves.

Horizons

Upper Cara- Districts

do- Ashgillian Species

ei an

Ringe- Oslo-Lange-

4ca 4c�-y 4d Sa 5b sund-rike Asker

Skien

Tancrediopsis planodorsata (Uirich, 1892) X X Ctenodonta dubia (Hall, 1847) X X Similodonta spjeldnaesi (H. & T. Soot-Ryen, 1960) X X Nuculites aff. planulatus Conrad, 1841 X X Nuculites sp. X X Cyrtodontula ventricosa (Hall, 1847) X X Cyrtodontula cf. truncata (Uirich, 1890) X X CyrtodQJ.Jtula sp. X X gen. & sp. uncertain X X Cyrtodonta sp. X X Ambonychia radiata (Hall, 1847) X X X X X Cleionychia corrugata (Lindstrom, 1880) X X Cleionychia pulchella (Lindstrom, 1880) X X Cleionychia cf. primitiva (Isberg, 1934) X X X X Cleionychia aff. rhomboidea Ulrich, 1892 X X Cleionychia sp. l X X Cleionychia sp. 2 X X Ambonychia sp. X X A pterineid (gen. and sp. uncertain) X X Semicorallidomus whitjieldi Isberg, 1934 X X Goniophorina volvens Isberg, 1934 X X Modiolopsis nilssoni (Hisinger, 1837) X X X X Modio[opsis leptaenarum Isberg, 1934 X X Modiolopsis exilis Billings, 1874 X X Cuneamya sp. l X X Cuneamya sp. 2 X X Cuneamya sp. 3 X X Gen. & sp. uncertain X X

Material. - One left valve (PMO 10070).

Locality and horizon.- Western point of FrognØya, Ringerike district. Stage

4ca, Lower Tretaspis Shale, Upper Caradocian.

Description. - Although no internal structure is observed, the present speci­

men is related to Ulrich's species according to its peculiar outline: Posterior

side long with subacute extremity and almost straight dorsal side; anterior

end rounded; ventral margin broadly convex with a more strongly convex

anterior edge; surface with fine concentric and a few stronger growth lines.

138 R. T. TONI

The Norwegian specimen is 10 mm long and 6 mm high. T. planodorsata has been recorded from the upper third of the Trenton shales of Minnesota. The present species differ from T. gibberula (Salter 1859) and T. contracta

(Salter 1859) by its longer and more straight posterior side.

Genus Ctenodonta Salter, 1852 Type species. - Tellinomya nasuta Hall 1847.

Ctenodonta dubia (Hall, 1847) Fig. 2, B D Tellinomya dubia Hall 1847: 153, pl. 34, fig. 6a-f.

Material. - Internal mold of a left valve (PMO 9717).

Locality and horizon. - Terneholmen, Asker, Oslo-Asker district. Stage 4c�, Upper Tretaspis Shale, Lowermost Ashgillian.

Remarks. - No remarkable difference is observed between the Norwegian species and that figured by Hall. They both share the following characters: Test subequilateral with a nearly central umbo, anterior extremity rounded, posterior one narrower with a slightly oblique truncation. Ornamentation and internal features are lacking in the present specimen. The Norwegian species is 11 mm long and 7 mm high, it is smaller than Hall's species. The present species is originally described from the Trenton Shale at Middleville, Trenton Falls, Herkimer and other places in New York.

Family PRAENUCULIDAE McAlester, 1968

Genus Similodonta Soot-Ryen, 1964 Type species. - Tellinomya similis Ulrich, 1892.

Similodonta spjeldnaesi (H. & T. Soot-Ryen, 1960) Fig. 2, C D Ctenodonta spjeldnaesi H. & T. Soot-Ryen 1960: 87, pl. 1, figs. 3-6, text-fig. l D Similodonta spjeldnaesi H. & T. Soot-Ryen 1964: 498.

Material. - One incomplete right valve (PMO 94018).

Locality and horizon. - Holmenskjæret at Holmen, Nesbru, Oslo-Asker district. Stage 5 a, Gastropod Limestone, Ashgillian.

Description.- Like the material described by H. & T. Soot-Ryen, the present specimen possesses a small rounded triangular shell, a slightly inflated umbo, a curved antero-dorsal margin, a rounded ventral margin; the posteroventral corner is broadly rounded; the posterodorsal margin is straight to concave with a protruding lower part; surface with broadly spaced concentric lines, mainly after the middle part of the shell.

The holotype is from stage 4by, Upper Chasmops Shale, Vestbråten,

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 139

Ringerike district. S. recurva (Ulrich 1892) and S. intermedia (Ulrich 1892)

are sirnilar to the present species in the gross overall morphology, but the

difference is mainly based on the shape of the posterior side and on binge

characters.

Family MALLETIIDAE Adams & Adams, 1858

Genus Nuculites Conrad, 1841 Type species.- Nuculltes oblongatus Conrad, 1841.

Nuculites aff. planulatus Conrad, 1841 Fig. 2, D & E O aff. Nuculites planulatus Conrad 1841: 68 O aff. Cleidophorus planulatus Hall 1847: 300, pl. 82, figs. 9a-e O aff. Cleidophorus planulatus McCoy 1855: 273, pl. lk, fig. 9 O aff. Nuculites (Cleidophorus) planulatus Pojeta 1971: pl. 6, figs. l, 2.

Material. - One intemal mold with a portion of the shell (PMO 8797).

Locality and horizon. - Temeholmen, Nakholmen, Oslo-Asker district. Stage 4ca, Lower Tretaspis Shale, Upper Caradocian.

Affinities and differences. - The Norwegian specirnen shares the following

characteristic features with Conrad's species: Test uniformly and slightly

convex; intemal septum extends to half way to the ventral margin; postero­

umbonal ridge well defined; a compressed area from the ridge to the dorsal

margin is easily detected. The present specirnen, however, shows a broader

and more rounded posterior side and the general outline is shorter than in N. planulatus. The Norwegian species is much more sirnilar to the one

figured by McCoy (1855). It has, as the British species, a strong oval anterior

muscle scar. In addition, six umbonal scars are clearly observed in the pres­

ent east. Surface with fine concentric lines. It is 16 mm lang and 8 mm high.

The present species differs from N. neglectus Hall, 1847 by its broader posterior side and by a more prominent umbonal ridge. N. planulatus is originally described from the Lorraine and Utica, New York, by Conrad (1841) as well as from the Schists of Keeper's Lodge, Goldengrove and

Llandeilo, U.K., by McCoy (1855).

Nuculites sp. Fig. 2, F

Material. - One bivalve extemal mold (PMO 9760).

Locality and horizon. - Frognøya, Ringerike district. Stage 4ca, Lower

Tretaspis Shale, Upper Caradocian.

Description.- Test elongate to orbicular; umbo nearly central; posterior side

obliquely truncate; a rounded ridge extends from the umbo to the posterior angle of the ventral margin; intemal septum curved towards the anterior

side; surface with fine and not clear concentric striae.

140 R. T. TONI

UPPER ORDOVICIAN DIVALVES FROM OSLO REGION 141

The Norwegian species may be related to N. cawdori (Sowerby, 1839). It has the same position of umbo and a similar rounded ridge from the umbo to the posterobasal margin. The present species, however, is higher and has a curved and not oblique internal septum. The Norwegian species is 15 mm lang and 12 mm high.

Family CYRTODONTIDAE Ulrich, 1894

Genus Cyrtodontula Tomlin, 1931 Type species. - Whitella obliquata Ulrich, 1890.

Cyrtodontula ventricosa (Hall, 1847) Fig. 2, G, H D Edmondia ventricosa Hall 1847: 155, pl. 35, figs. 1a-f D Cypricardites ventricosa Miller 1889: 477 D Bodmania ventricosa Miller & Faber 1894: 24 D White/la ven­tricosa Ulrich 1894: 573, pl. 41, figs. 24-26 D White/la ventricosa Grabau & Shimer 1909: 415, fig. 536, e, f.

Material. - One external mold (PMO 55861).

Locality and horizon. - Frognøya, Ringerike district. Stage 4da, Lower lsotelus Shale, Ashgillian.

Description. - Shape rhomboidal, clearly ventricose; umbo large and prom­inent; hinge line seems to be short and from its posterior extremity, the shell slopes abruptly towards the ventral margin; surface with fine concen-

Fig. 2. A. Tancrediopsis planodorsata (Ulrich, 1892). Lateral view of a left valve. X 4. Stage

4ca, western point of Frognøya, Ringerike district. (PMO 10070). Coll. Kiær 1915. B. Ctenodonta du bia (Hall, 1847). Lateral view of a mold of a left val ve. X 5. Stage

4cp, Temeholmen, Oslo-Asker district. (PMO 9717). Coll. BrØgger 1886. C. Similodonta spjeldnaesi (H. & T. Soot-Ryen, 1960). Lateral view of an incomplete

right valve. X 5. Stage 5a, Holmenskjæret at Holmen, Oslo-Asker district. (PMO 94018). Coll. Bockelie 1965.

D, E. Nuculites aff. planulatus Conrad, 1841. D - lateral view of a left valve; E -umbonal view. X 4. Stage 4ca, Temeholmen, Oslo-Asker district. (PMO 8797). Coll. Brøgger 1912.

F. Nuculites sp. Right lateral view of a bivalved specimen. X 3. Stage 4ca, Frognøya, Ringerike district. (PMO 9760). Coll. Kiær 1914.

G, H. Cyrtodontula ventricosa (Hall, 1847). G - anterior view; and H - lateral view of a left val ve. X 2. Stage 4da, Frognøya, Ringerike district. (PMO 55861). Coll. Kiær 1916.

l, J. Cyrtodontula cf. truncata (Ulrich, 1890). I - lateral view; and J - anterior view of the extemal mold of a right valve. X 3. Stage 5a, Holmenskjæret at Holmen, Oslo­Asker district. (PMO 94015). Coll. Bockelie 1965.

K, M. Cyrtodontula sp. K - lateral view; L - anterior view; and M - posterior view of a right val ve. X 2. Stage 5a, Stavnestangen, Ringerike district. (PMO 13836). Coll. Kiær 1915.

N. Cyrtodonta sp. Lateral view of a left val ve. X 3. Stage 5a, Vestre Svartøya, Ringerike district. (PMO 94036). Coll. Kiær 1913.

O. A cyrtodontid (gen. & sp. uncertain). Lateral view of a right val ve. X 3. Stage 5a, Herøya in Porsgrunn, Langesund-skien district. (PMO 13193). Excursion 1915.

P. Cleionychia corrugata (Lindstri:im, 1880). Lateral view of a right valve. X 5. Stage 5a, Stavnestangen, Ringerike district. (PMO 15667). Coll. Kiær 1915.

142 R. T. TONI

tric striae; anterior margin sharply rounded above, making, as stated by Hall (1847: 156), a cordiform profile and is in 'almost a line with the umbo'; umbonal ridge weak.

C. rugatine (Ulrich, 1894) and C. concentrica (Ulrich, 1894) have a much larger anterior side.

C. ventricosa was originally described from the central and higher parts of the Trenton Limestone at Middleville, Herkimer, Trenton Falls and Lo­wille, New York.

Cyrtodontula cf. truncata (Ulrich, 1890) Fig. 2, l, J D cf. Whitella truncata Ulrich 1890: 385 D cf. Whitella truncata Ulrich 1892: 572, pl. 41, figs. 10--14.

Material. - One external mold of a right valve (PMO 94015).

Locality and horizon. - Holmenskjæret at Holmen, Oslo--Asker district. Stage Sa, Gastropod Limestone, Ashgillian.

Description. - The Norwegian specimen is more or less identical to Ulrich's species. It has a subrhomboidal, oblique and ventricose shell; umbo promi­nent, strongly incurved and nearly terminal; umbonal ridge angular and extends to the posterobasal angle; anterior and posterior slopes, slightly con­vex and abrupt; anterior side very short and narrowly rounded; posterior one truncated; surface with fine concentric lines and stronger irregular ones; distance from umbo to the posterobasal angle is 21 mm and the maximum length is 17 mm.

C. truncata differs from C. scofieldi (Ulrich, 1892) in being more convex and in having a shorter anterior side and a truncated posterior one.

C. truncata has been described from the Galena Shales in Goodhue county, Minnesota.

Cyrtodontula sp. Fig. 2, K-M

Material. - One right valve (PMO 13836).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - Shell obliquely ovate and elongate; posterior side nearly straight and narrow, anterior one very small; umbo prominent and incurved; umbonal ridge sharp and extends from the umbo to the posterobasal extrem­ity; anterior slope convex and the posterior is flat to concave. In general, the specimen looks distorted. Surface with fine concentric striae. The internal features are not observed. The maximum height measured from the umbo to

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 143

the posterobasal extremity is 35 mm and the maximum length is 19 mm. The present specimen may be related to C. sterlingensis (Meek & Wor­

then, 1870). It has the same obliquely elongate shape, but differs by a less angular umbonal ridge and straighter posterior side. The Norwegian species is also smaller in size.

Genus Cyrtodonta Billings, 1858 Type species. - Cyrtodonta rugosa Billings, 1858.

Cyrtodonta sp. Fig. 2, N

Material. - One mold showing extemal and internat features (PMO 13193).

Locality and horizon. - Herøya in Porsgrunn, Langesund-Skien district. Stage Sa, Gastropod Limestone, Ashgillian.

Description. - Test very inequilateral, slightly convex; posterior side higher than anterior one; surface with concentric lines and clearly defined growth lines. A small elongated anterior muscle scar is clearly seen.

Genus uncertain Fig. 2, O

Material. - Seven molds (PMO 94036, 94025, 94026, 94027, 94028, 94029, 94030). The specimen figured is 94036.

Locality and horizon. - Vestre Svartøya, Ringerike district; Holmenskjæret at Holmen, Oslo-Asker district. Stage Sa, Gastropod Limestone, Ashgillian.

Description. - Shell tumid, elongated dorsoventrally; anterior extremity sub­angular; a part of the recrystallized shell in the specimen figured shows that it was thin. These characters relate the Norwegian specimens to a cyrto­dontid. But due to their bad preservation and lack of intemal features, gen­erle identification is uncertain.

Family AMBONICHIIDAE Miller, 1877

Genus Ambonychia Hall, 1847 Type species. - Ambonychia radiata Hall, 1847.

Ambonychia radiata Hall, 1847 Fig. 3, A, B D Ambonychia radiata Hall 1847: 292, pl. 80, figs. 4a-b D Byssonychia radiata Ulrich 1894: 477, fig. 35, VI D Byssonychia radiata Pojeta 1962: 201 D Ambonychia radiata Pojeta 1966: 147, pl. 10 D Ambonychia radiata Pojeta 1971: pl. 10, figs. 10, 11.

Material. - Five right valves (PMO 14312, 16503, 17196, 20715, 20717),

144 R. T. TONI

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 145

one left valve (PMO 14303), two internal molds (PMO 16385, 20716), two bivalved molds (PMO 13306, 17195) and five incomplete molds (PMO 14306, 14307, 14310, 16404, 17194). The specimens figured are 14303 and 16503.

Locality and horizon. - South beach of Vestre Svartøya, Ringerike district; Holmenskjæret at Holmen, Tangen, Semsvannet, Jongskollen and Slependen in the Oslo-Asker district; Porsgrunn, Langesund-Skien district. Stage Sa, Gastropod Limestone, Ashgillian and stage 5b, Calcareous Sandstone forma­tion, Upper Ashgillian.

Occurrence. - Originally described from the Lorraine Formation of New Y ork. Recorded from the Maysville-Richmond in Quebec, Canada, also in Turin, ltaly; and from Ohio, Indiana, Kentucky, Virginia and Tennessee, U.S.A. It is further recorded by Hind (1910) from the Drummuck Group, Scotland.

Remarks. - This well known and widely distributed species is a common form in the Norwegian collection. The specimens at hand show the same characters as Hall's species: Raised and incurved umbo, nearly obsolete anterior margin, obliquely truncate posterior side making an obtuse angle with the hinge line. The Norwegian species, however, seems to be larger than the American one. The specimen in Fig. 3, B has approximately fifty radial plications and is 29 mm long and 35 mm high.

Fig. 3. A, B. Ambonychia radiata Hall, 1847. A - lateral view of a left val ve. X 2. Stage Sa,

Vestre Svartøya, Ringerike district. (PMO 14303). Coll. Miinster 1891; B - posterior view of a right val ve. X 2. Stage Sa, Vestre SvartØya, Ringerike district. (PMO 16S03). Coll. Kiær 191S.

C. Cleionychia pulchella (Lindstrom, 1880). Lateral view of a right val ve. X 2. Stage Sa, Stavnestangen, Ringerike district. (PMO 1S6S4). Coll. Kiær 191S.

D. Cleionychia cf. primitiva (Isberg, 1934). Lateral view of left valve. X 3. Stage Sa, Nostret, Sælabon, Ringerike district. (PMO 9403S). Coll. Kiær 1914.

E. Cleionychia aff. rhomboidea Ulrich, 1892. Lateral view of an external right valve mold. X%. Stage Sa, Holmenskjæret at Holmen, Oslo-Asker district. (PMO 94020). Coll. Bockelie 196S.

F. Cleionychia sp. l. Lateral view of a right val ve. X 2. Stage Sa, Nostret, Sælabon, Ringerike district. (PMO SS86S). Coll. Kiær 1916.

G. Cleionychia sp. 2. Lateral view of a left valve external mold. X 2. Stage Sb, Hol­menskjæret at Holmen, Oslo-Asker district. (PMO 94019). Coll. Bockelie 1963.

H. Ambonychia sp. Bivalved specimen. X3. Stage Sa, Vestre Svartøya, Ringerike district. (PMO 14316). Coll. Miinster 1891.

l. A pterineid (gen. & sp. uncertain). Lateral view of an external mold of a left valve. X 3. Stage 4ca, Frognøya, Ringerike district. (PMO 10280). Coll. Kiær 191S.

J. Semicorallidomus whitfieldi Isberg, 1934. Lateral view of a right val ve. X 2. Stage Sa, Stavnestangen, Ringerike district. (PMO 1S696). Coll. Kiær 191S.

K. Goniophorina volvens Isberg, 1934. Lateral view of an incomplete left valve. X 3. Stage Sa. Stavnestangen, Ringerike district. (PMO 17823). Coll. Kiær 191S.

L. M odiolopsis nilssoni (Hisinger, 1837). Lateral view of a left val ve. X 3. Stage Sa, Nostret, Sælabon, Ringerike district. (PMO SS868). Coll. Kiær 1914.

146 R. T. TONI

Genus Cleionychia Ulrich, 1892 Type species. - Ambonychia lamellosa Whitfield, 1882.

Cleionychia corrugata (Lindstrom, 1880) Fig. 2, P O Ambonychia corrugata Lindstrom 1880: 17, pl. 15, figs. 1-5 O Ambonychinia cor­rugata Isberg 1934: 55, pl. 4.

Material. - One small right valve (PMO 1S667).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - The present specimen shares the following characters with Isberg's material: Anterior side curved; posterior one winged; umbo small, pointed and somewhat curved; concentric ondulations clear, widely spaced with fine striae in between. The valve figured is 7 mm lang and 6 mm high.

C. undulata (Isberg, 1934) (Isberg, pl. S, fig. la--c) is more or less similar in outline to the Norwegian specimen, but the latter has stronger undulations.

C. corrugata was originally described from the Bada Limestone, Dalarna, Sweden.

Cleionychia pulchella (Lindstrom, 1880) Fig. 3, C OAmbonychia pulchella Lindstrom 1880: 17, pl. XIII, figs. 47-50 O Ambonychinia pulchella Isberg 1934: 59, pl. 5, figs. 2a-d.

Material. - One external mold (PMO 15654).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - No significant differences were observed between the Nor­wegian specimen and the Swedish material: Test convex, binge line straight and lang, umbo terminal and pointed, the part of the ventral margin which is diagonal to the umbo is semi-circular; posterior side slightly winged; surface with concentric lines. The present specimen is 23 mm lang and 20 mm high. The particular shape of the ventral margin and the posterior side differen­tiates C. pulchella from any other species of Cleionychia.

The present species is originally described from the Bada Limestone, Dalarna, Sweden.

Cleionychia cf. C. primitiva (Isberg, 1934) Fig. 3, D O cf. Ambonychinia primitiva Isberg 1934: 39, pl. l, figs. la-c.

Material. - Four extemal molds of left valves (PMO 9403S, 10679, 1S31S,

UPPER ORDOVICIAN BIVALVES .FROM OSLO REGION 147

16386); two extemal molds of right valves (PMO 15262, 15200). The sped­men figured is 94035.

Locality and horizon. - Sælabon, Stavnestangen, south beach of Svartøya and Frognøya, Ringerike district; Holmenskjæret at Holmen in Nesbru, Oslo -Asker district. Stage 4da, Lower Isotelus Shale, Ashgillian.

Affinities and differences. - The following characters are common to both Isberg's species and the present one: Test convex, hinge line long and straight, anterodorsal margin at right angles to the hinge line, anteroventral margin curved, posterodorsal margin concave to straight, posterior extremity winged, umbo small, terminal and dipping in the hinge area; surface with fine concentric lines. The specimen figured is 13 mm long and 13 mm high.

The Norwegian specimens, however, show stronger concentric lines near the ventral margin. In the specimen figured clear posterior lateral teeth are observed on the posterior extremity of the hinge line.

C. primitiva may be related to C. skalbergensis Isberg (1934) (Isberg, 1934, pl. I, figs. 2a-c), but this latter has different hinge structure, more curved umbo and more fine omamentation. C. primitiva is described from the Leptaenakalk, Dalarna, Sweden.

Remarks. - The specimen figured is incorrectly oriented. The dorsal margin should be parallel to the horizontal.

Cleionychia aff. C. rhomboidea (Ulrich, 1892) Fig. 3, E D aff. Clionychia rhomboidea Ulrich 1892: 97 D aff. Clionychia rhomboidea Ulrich 1894: 496, pl. 35, figs. 19, 20 D aff. Cleionychia rhomboidea Pojeta 1966: 120, pl. 21.

Material. - One extemal mold (PMO 94020).

Locality and horizon. - Holmenskjæret at Holmen in Nesbru, Oslo-Asker district. Stage Sa, Gastropod Limestone, Ashgillian.

Affinities and differences. - The present specimen agrees with Ulrich's species in the following characters: Test very oblique and rhomboidal; ven­tral side convex; anterior side nearly straight; posterior side produced and narrowly curved; anterior slope more abrupt than posterior one; greatest convexity nearly in the middle of the shell; surface with concentric lines. Intemal features are not observed. However, the Norwegian specimen ap­pears to be more convex and the umbo is more prominent and more strongly incurved. According to Ulrich, the posterior side of C. rhomboidea is more produced and more narrowly curved than any other.

Cleionychia species Cleionychia rhomboidea was originally described from the Lower Limestone of the Trenton Formation at Minneapolis, Minnesota.

148 R. T. TONI

Cleionychia sp. l Fig. 3, F

Material. - One right valve (PMO 55865) and an extemal mold of a right valve (PMO 10497). The specimen figured is 55865.

Locality and horizon. - Nostret, Sælabon and Frognøya, Ringerike district. Stage 4d, Isotelus beds and stage Sa, Gastropod Limestone, Ashgillian.

Description. - Shell convex, mainy on the umbonal region and near the anterior side, where the slope to the edge is abrupt; beak terminal, pointed and incurved; hinge line straight; posterior margin curved; anterior one straight; ventral margin broadly curved; surface with numerous concentric lines. Intemal features not observed. The specimen figured is 27 mm long and the distance from umbo to maximum convexity of the ventral margin is 33 mm.

Discussion. - The Norwegian form may be related to C. pulchella (Lind­stram, 1880) in having a nearly similar outline. However, it has a more curved posterior margin, more sharply bent anterior one and a more broadly curved ventral margin. Comparison is also made with Cleionychia sp. A, described by H. & T. Soot-Ryen (1960: 106, pl. 3, fig. 43). Both species share the same type of omamentation and the same shape of anterior mar­gin, but the specimens at hand are more convex and have a more widely curved ventral margin.

Cleionychia sp. 2 Fig. 3, G

Material. - One extemal mold of a left valve (PMO 94019).

Locality and horizon. - Holmenskjæret at Holmen in Nesbru, Oslo-Asker district. Stage Sb, 'Calcareous Sandstone Formation', Upper Ashgillian.

Description. - Test very inequilateral; anterior side nearly obsolete and slopes rapidly in a straight line to the ventral margin, which is slightly curved; posterior side alate; hinge line long and straight; umbo terminal and incurved; surface with widely spaced concentric lines with finer intervening ones; a radial impression from the umbo to the posterobasal margin is clearly detected; intemal features not observed. The present species is 43 mm long and 20 mm high.

Remarks. - The Norwegian form may be related to Ambonychinia magna

Isberg, 1934 (Isberg, 1934, pl. 6, figs. la-b). However, it is less convex and less high than Isberg's species. Also, apart from the umbonal radial impres­sion, the radial striae of the Swedish species are not observed.

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 149

Ambonychia sp. Fig. 3, H

Material. - Two deformed bivalved molds (PMO 14311, 14316). The sped­men figured is 14316.

Locality and horizon. - Vestre Svartøya, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - The Norwegian specimens look distorted. Outline triangular, beaks moderate and incurved, posterior side winged, anterior one abrupt, surface with simple ribs.

The general outline of the Norwegian species may relate it to an Opithop­

tera, but as mentioned by Pojeta (1966), the simple ribs of the specimens at hand differentiates them from Opithoptera, which has bifurcated ribs.

Family PTERINEIDAE Miller, 1877

Genus and sp. uncertain Fig. 3, I

Material. - One extemal mold of a left valve (PMO 10280).

Locality and horizon. - Western point of Frognøya, Ringerike district. Stage 4ca, Lower Tretaspis Shale, Upper Caradocian.

Remarks. - The present mold has the general shape of a pterineid. Test convex, umbo anterior, surface with concentric growth rings. But since no intemal features are observed, generic identification is uncertain.

Family MODIOMORPHIDAE Miller, 1877

Genus Semicorallidomus Isberg, 1934 Type species. - Semicorallidomus whitfieldi Isberg, 1934.

Semicorallidomus whitfieldi (Isberg, 1934) Fig. 3, J D Semicorallidomus whitfieldi Isberg 1934: 180, pl. 16, figs. 9a-c D Semicorallidomus whitfieldi Moore (ed.) 1969: 397, figs. D4, 2.

Material. - One right valve (PMO 1S696).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - The Norwegian specimen is larger than the Swedish one. It also represents the right valve, which was not described by Isberg. More­over, one can observe the main characters of the original species: Shell slightly convex and thick; inequilateral with a pear-shape lateral outline;

150 R. T. TONI

posterior side higher than anterior one; ligamental area long and narrow; anterior side small with an obsolete lunule; surface with sharp concentric lines. The Norwegian species is 18 mm long and 14 mm high.

S. hians Isberg, 1934 (Isberg, 1934, pl. 16, figs. 10a-b) has a terminal umbo and more widely spaced concentric lines. S. whitfieldi is originally described from the Leptaenakalk, Dalarna, Sweden.

Genus Goniophorina Isberg, 1934 Type species.- Goniophorina volvens Isberg, 1934

Goniophorina volvens (Isberg, 1934) Fig. 3, K O Goniophorina volvens Isberg 1934: 205, pl. 27, figs. 6a-b and pl. 28, figs. la-c O Goniophorina (Goniophorina) volvens Moore (ed.) 1969: 395, fig. D2, 10.

Material. - One incomplete left valve (PMO 17823).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - Although not complete, the present specimen shows the char­acteristic features of lsberg's species. Shell thin, rhomboidal to trapezoidal in shape; strongly convex; posterior basal extremity angular; umbonal carena, from beak to posterobasal angle sharp and compressed; umbo large, anterior, curved inward and forward; surface with fine concentric lines.

G. (G.) volvens shows resemblance to G. (Cosmogoniophorina) carinata

Isberg (Isberg, 1934, pl. 27, figs. 3-S). Both species share a similar outline and umbonal carina. But G. (C.) carinata has radial costae.

G. (G.) volvens is originally described from the Leptaenakalk, Dalarna, Sweden.

Genus Modiolopsis Hall, 1847 Type species.- Pterinea modiolaris Conrad, 1838.

Modiolopsis nilssoni (Hisinger, 1837) Fig. 3, L O Modiola nilssoni Hisinger, Leth. Svec. 1837: pl. 18, fig. 13 O Modiolopsis nilssoni McCoy 1855: 267, pl. 11, fig. 21 O Modiolopsis nilssoni Kjerulf 1865: 11, fig. 27.

Material. - One left valve (PMO SS868), seven external molds (PMO 11044, 11672, 11839, 11840, 118S1, 11842, 20468) and seven external casts (PMO 11843). The specimen figured is SS868.

Locality and horizon. - Hovedøya, Oslo-Asker district and Nostret, Sælabon, Ringerike district. Stage Sa, Gastropod Limestone, and stage Sb, 'Calcareous Sandstone Formation', Ashgillian.

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 151

Remarks.- No special difference is detected between the specimens at hand

and those figured by McCoy and Kjerulf. The test is narrowed in front and

broadened posteriorly; ventral margin is nearly straight with a wide shallow

sinus about the middle, from which a slight concavity extends towards the

umbo; surface with fine unequal concentric striae. The specimen figured is

18 mm long and 9 mm high.

McCoy mentioned that M. antiqua Sowerby, 1839, which is only shorter

and not gaping', is a synonym of the present species. M. nilssoni with Ambo­

nychia radiata Hall are the most common species in the Norwegian collec­

tion.

McCoy recorded M. nilssoni from the Ludlow shales, Ludlowian, England

and Kjerulf recorded it from stage 4, Llanvinian-Ashgillian at Hovedøya,

Norway.

Modiolopsis leptaenarum (Isberg, 1934) Fig. 4, A D Modiolopsis leptaenarum Isberg 1934: 158, pl. 26, figs. la-c.

Material.- Five extemal molds of right valves (PMO 94032, 14304, 16182,

18132, 94034); two extemal molds of left valves (PMO 94009, 94034). The

specimen figured is 94032.

Locality and horizon. - Ø. Nes badestrand and Holmenskjæret at Holmen

in Nesbru, Oslo-Asker district. Stage Sa, Gastropod Limestone, Ashgillian.

Description. - The Norwegian specimens share the following characters with

the Swedish species: Shell obliquely elongate, moderately convex; anterior

side very small; posterior side larger and higher; umbo prosogyral and in­

curved; umbonal carena weak; hinge line long; ventral margin nearly straight;

surface with clear concentric lines. The specimen figured is 11.5 mm long and 6 mm high.

M. leptaenarum is very similar to M. oweni Ulrich, 1894 (Ulrich, 1894: 506, pl. 42, figs. 15, 16); it differs only in the following ways: Ringe line

longer, anterior side shorter and more convex. Comparison is, also made with M. pygmaea Isberg, 1934 (Isberg, 1934: 159, pl. 26, figs. 2a-b) from

which it differs in being less convex and in having a less high posterior side.

M. leptaenarum is originally described from the Leptaenakalk, Dalarna,

Sweden.

Modiolopsis exilis (Billings, 1874) Fig. 4, B, C D Modiolopsis exilis Billings 1874: 132, pl. 8, figs. 5, Sa D Modiolopsis ruda Billings 1874: 133, pl. 8, fig. 6 D Modio!opsis exilis McLearn 1924: 125, pl. 18, figs. 15-17, pl. 19, fig. 16.

Material. - One bivalved specimen (PMO 94014) and an incomplete right

valve (PMO 94008).

152 R. T. TONI

Fig. 4. A. Modiolopsis leptaenarum Isberg, 1934. Lateral view of an external mold of a right

valve. X 4. Stage 5a, Holmenskjæret at Holmen, Oslo-Asker district. (PMO 94032). Coll. Bockelie 1965.

B, C. Modiolopsis exilis Billings, 1847. B - lateral view of a bivalved specimen. X2. Stage 5a, Holmenskjæret at Holmen, Oslo-Asker district. (PMO 94014). Coll. Bockelie 1966; C - lateral view of a right val ve. X 3. Stage 5a, from the same locality. (PMO 94008). Coll. Bockelie 1965.

D. Cuneamya sp. 1. Lateral view of a right val ve. X 3. Stage 5a, Vestre Svartøya, Ringerike district. (PMO 13947). Coll. Mi.inster 1891.

E. Cuneamya sp. 2. Lateral view of a right valve. X 2. Stage 5a, Vestre Svartøya, Ringerike district. (PMO 13948). Coll. Miinster 1891.

F. Cuneamya sp. 3. Lateral view of a bivalved specimen. X2. Stage 5a, Nyborg, Asker, Oslo-Asker district. (PMO 11065). Coll. Kjerulf 1868.

G. Gen. & sp. uncertain. Lateral view of a right valve, external mold. X 3. Stage 5a, Stavnestangen, Ringerike district. (PMO 15940). Coll. Kiær 1915.

Locality and horizon. - Holmenskjæret at Holmen in Nesbru, Oslo-Asker

district. Stage Sa, Gastropod Limestone, Ashgillian.

Description. - Shell transverse; binge line nearly straight; ventral margin

broadly convex and curved at each extremity; beaks large, prosogyral and in­

curved; anterior side small, narrowly rounded to subangular above; posterior

side broadly rounded to subtruncate; umbonal angulation rounded; surface

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 153

with concentric ridges which are stronger at the anterior end. The bivalved

specimen is 18 mm long and 9 mm high.

Discussion. - The previous characters agree more or less with Billings's de­

scription for this species. The Norwegian specimens are shorter, however.

But, as mentioned by McLearn (1924), M. exilis is very variable. According

to McLearn M. ruda and M. exilis are one and the same species due to the

infinite variations which they undergo. M. solenoides Sowerby, 1839, differs

in having the dorsal and ventral margins more closely parallel. M. leightoni

Williams 1913, shares with M. exilis a great variability, but is always shorter.

M. exilis was originally described from the Silurian, Arisaig, Nova Scotia.

Family GRAMMYSIIDAE Miller, 1877

Genus Cuneamya Hall & Whitfield, 1875 Type species. - Cuneamya miamiensis Hall & Whitfield, 187S

Cuneamya sp. 1 Fig. 4, D

Material. - One right valve (PMO 13947).

Locality and horizon.- Vestre Svartøya, Ringerike district. Stage Sa, Gastro­

pod Limestone, Ashgillian.

Remarks. - Badly preserved specimen. The following characters relate it to a Cuneamya species: Shell subrhomboidal; strongly incurved beaks; obliquely

truncate posterior margin; anterior surface with clear, uniform concentric

ornamentation.

Cuneamya sp. 2 Fig. 4, E

Material. - Two deformed external molds (PMO 13948, 13949). The sped­

men fig\lred is 13948.

Locality and horizon.- Vestre Svartøya, Ringerike district. Stage Sa, Gastro­

pod Limestone, Ashgillian.

Description. - Test transversely elongate, oval; dorsal and ventral margins

nearly parallel; anterior side very short; lunule clear an oblique sulcus runs

from the umbones to nearly the middle of the ventral margin; concentric

ridges clear on the anterior side, faint on the posterior.

Discussion. - The previous characters relate the Norwegian specimens to

Cuneamya. However, the oblique sulcus may relate it to a Grammysia, and

154 R. T. TONI

the elongate shape may relate it to an Orthonauta. But, due to the bad pre­

servation and absence of internal features, the present specimens more prob­

ably belong to Cuneamya.

Cuneamya sp. 3 Fig. 4, F

Material. - One articulated specimen (PMO 1106S).

Locality and horizon. - Nyborg in Asker, Oslo-Asker district. Stage Sa,

Gastropod Limestone, Ashgillian.

Description. - Shape nearly triangular; umbo strongly incurved forward;

anterior side small and slightly projecting; shell ventricose along the nm­

banal ridge; concentric lines clearer on the anterior side; internal features

not observed.

Discussion. - The Norwegian specimen may be related to C. elliptica Miller

(in Foerste 1924: 132, pl. 17, fig. l) from which it differs in having a much

more oblique posterior margin. C. neglecta Meek (in Foerste 1924: 131, pl.

17, fig. 2) has a more upright anterior margin. C. miamiensis Hall & Whit­

field 187S, has nearly a similar posterior margin but a different shape of

anterior side.

Genus and sp. uncertain Fig. 4, G

Material. - One external mold of a right valve (PMO 1S940).

Locality and horizon. - Stavnestangen, Ringerike district. Stage Sa, Gastro­pod Limestone, Ashgillian.

Description. - Shape ovoid, slightly convex; umbo anterior, small and proso­

gyral; surface with somewhat irregular concentric ridges; internal features

not observed. Due to the bad preservation of the present specimen, exact

identification is not possible. The general outline may suggest a cyrtodontid.

Distribution and faunal assemblages Table l shows the distribution of the described species in the different hori­

zons and districts. Bivalvia are reported from only three districts: Ringerike,

Oslo-Asker and Langesund-Skien. Not a single specimen is recorded from

the Hadeland district, which is the fourth district where the Upper Ordovi­

cian is present. This may be d\le to a Jack of systematical sampling. On the

other hand, a rich fauna has been collected from stage Sa in the Ringerike

district. This is in accordance with what has been observed previously (Hen-

UPPER ORDOVICIAN BIVALVES FROM OSLO REGION 155

ningsmoen 1960), that the Gastropod Limestone (Sa) is typically developed

in Ringerike, where it is highly fossiliferous. Twenty-one species are reported

from this stage: Similodonta spjeldnaesi, Cyrtodontula cf. truncata, C. sp., a

cyrtodontid, gen. & sp. uncertain, Cyrtodonta sp., Ambonychia radiata,

Cleionychia corrugata, C. pulchella, C. cf. C. primitiva, C. aff. C. rhom­

boidea, C. sp. l, C. sp. 2, Ambonychia sp., Semicorallidomus whitjieldi,

Goniophorina volvens, Modiolopsis nilssoni, M. leptaenarum, M. exilis,

Cuneamya sp. l, C. sp. 2, C. sp. 3, gen. & sp. uncertain. Many forms of this

assemblage are described from the Leptaenakalk (Sweden) and the Upper

Drummuck Group (Scotland), which are believed to be contemporaneous

with stage Sa of Norway. Oslo-Asker district (thirteen species) shares Ringe­

rike district in this rich fauna. Langesund--Skien's share is only of two spe­

eies.

Only three species are recorded from the Calcareous Sandstone Formation

(Sb): Ambonychia radiata, Cleionychia sp. 2 and Modiolopsis nilssoni. Four

species are described from the Lower Tretaspis Shale (4ca): Tancrediopsis

planodorsata, Nuculites aff. planulatus, Nuculites sp. and a pterineid, gen.

uncertain. One species only, Ctenodonta dubia is recorded from the Tretaspis

Limestone (4c�) and the Upper Tretaspis Shale (4cy). In addition to the species reported here, many other fossil bivalves could

not be identified, due to their poor preservation. The Upper Ordovician

bivalve fauna of the Oslo Region could well have been richer and the species

might have a wider geographical and vertical distribution than the present

material shows. Unfortunately, the possibilities for finding hetter material

are small, due to the nature of the matrix in which the bivalvia are embedded

in this region.

Acknowledgements. - Professor G. Henningsmoen is gratefully thanked for providing me with research facilities at Paleontologisk Museum in Oslo. Dr. D. L. Bruton and Mr. J. F. Bockelie have kindly assisted me with certain aspects of the preparation and photographing of the material.

June 1974

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