76 



PALEONTOLOGY OP NEW-YORK. 



Position mid locality. This species occurs in the lower part of the group at Flarnborough 

 head, Canada West. {Stau ColUciiu?!..) 



464. 35. ATRYPA NAVIFORMIS. 



Pl. XXIV. Fig. \a-k. 

 Atrypa namformis. Hall,, Geol. Rep. 4th Dist. N. York, 1843, pag. 71, fi^. 3. 



Shell ovoid, gibbous, both valves very convex ; dorsal valve much elevated, and angulated 

 or subcarinated towards the beak ; beak very strongly incurved ; base extremely elevated, and 

 extended into a linguiform process filling a deep sinus in the ventral valve ; ventral valve 

 very convex, and angulated towards the beak ; surface marked by fine concentric lines and 

 more distant elevated imbricating lines of growth, longitudinally marked by radiating strise, 

 which, on old shells, become quite conspicuous t )v/ards the margin ; young shells wdth the fine 

 concentric and radiating striee rather inconspicuous, and the lines of growth very prominent. 



This species, though in general form approaching several others in the group, is nevertheless 

 very distinct. In old shells the valves are very gibbous, and subangulated towards the beak. 

 The beak of the dorsal valve is more extremely incurved, and the front very perfectly con- 

 tinued into a linguiform process, which does not occur in the follov/ing species, nor in those of 

 similar forms in the Niagara group. It is further distinguished by longitudinal striae, which are 

 quite conspicuous towards the margins of the valves in old shells. Its greater proportional 

 width distinguishes it from the succeeding species, while its great depth and elevated front at 

 once distinguish it from A. intermedia. It should not be forgotten, however, that in young shells 

 the elevated front is not a characteristic feature, a slight indentation or sinus only being ob- 

 servable. 



Fig. 1 a. View showing the ventral valve, with the elevated beak of the dor?al valve. 

 Fig. 1 b. View of the dorsal valve of a full grown shell. 

 Fig. 1 c, d. Front and cardinal view of the same shell. 

 Fig. 1 e. Profile view of the same. 

 Fig. 1 /. A portion of the surface enlarged. 



^^^- 1 S^ ^1 i-> ^'- Several views of a young shell, the front 1 2, showing a scarcely formed sinus, 

 contrasting in this respect very strongly with fig. 1 c. 



Position and locality. In the upper limestone of the group at Sodus point, and in the same 

 position at Rochester ; it has been rarely seen in other localities. (State Collection.) 



465. 36. ATRYPA CYLINDRICA («. sp.). 



Pl. XXIV. Fig.2a-h. 

 Shell elongated, cylindrical, gibbous, viddth and depth equal ; valves nearly equally convex, 

 beak of the dorsal one much- extended beyond and incurved over the beak of the ventral 

 valve ; dorsal valve moderately elevated in front, centre flat, or with a slight undefined de- 



