27G 



PALiONTOLOGY OF NEW-YOEK. 



635. 49. ATRYPA BIDENTATA. 



Pl. LVII. Fig. 3o-A. 



Terehratula bidentata. Hisinger, Vet. Acad. Handl. 182G, p. 343, t. vii, f. 5. 



— — Idem, Anteckn. iv, tab. vii, figf. 5. 



— — Dai-man, Vet. Acad. Handl. 1827, pag. 142, tab. vi, fif. 5. 



— — Hisinger, Petref. suecica, pag. 81, pl. xxiii, fig. 7. 



— — SowKRBY : MuRCHi.80N's Sil. System, 1839, pag. 625, pl. 12, fig. 13 a- 



Triangular ; beak of dorsal valve acute, ami extended in a nearly straight line ; valves 

 unequal, llie ventral one more convex ; strongly plicated, with one or two of the plications 

 depressed on the dorsal and elevated on the ventral valve ; a foramen beneath the apex of the 

 beak of the dorsal valve. 



A comparison with the Swedish specimens shows no appreciable difference of character 

 between our specimens and one there known as Tercbratula bidentata. Tlic allied form in the 

 Clinton group is quite distinct from this one, as already shown, and must be regarded as another 

 species. We have moreover knowledge of the fact that it occurs in the same association here 

 as at Dudley in England, and Gothland in Sweden. 



This species, in the young state, may be easily confounded with Jllrypa negleda ; but the 

 plications are less numerous and more angular, and the beak nearly straight and more ex- 

 tended, and its proportional width is usually greater. 



Fig. 3 a, h. Ventral and dorsal views of the same specimen, 



Fisf. 3 c, d. Similar views of a larger individual. 



Fig. 3 e, f. Profile views of a young and old individual. 



Fig. 3 g. Front view of a specimen, showing the sinus and slight elevation. 



Fig. 3 h. Several plications enlarged to show the surface markings. 



Position and locality. In the shale at Lockport. 



636. 50. ATRYPA CUNEATA. 



Pl. LVII. Fig. 4 o - r. 



Terehratula cuneata. Dalman, Vet. Acad. Handl. 1827, pag. 141. tab. vi, fig. 3. 



— — HtsiNGER, Petrif. Suecica, 1837, p. 81, t. xxiii, f. 5. 



— — SowEUBT : MuRCHisoN, Sil. System, pag. 625, pl. 12, fig. 13. 



Triangular or cuneiform, proportions of width and length variable, usually depressed, pli- 

 cated ; plications ten to twelve, strong, simple, diverging from the beak, and the lateral ones 

 curved towards the margin, three or four central ones depressed on the dorsal valve and 

 elevated on the ventral valve ; crossed by filiform striae, and sometimes by a few stronger 

 imbricating lines of growth ; beak of dorsal valve nearly straight and extended beyond the 

 ventral valve, perforated at the extremity. 



This shell presents considerable variety of form and proportions ; but after an examination 

 of a large number of specimens, I am unable to find differences on which to found a specific 



