76 
PALEONTOLOGY OF NEW-YORK. 
Position and locality. This species occurs in the lower part of the group at Flamborough 
head, Canada West. ( state Collection.) 
464. 35. ATRYPA NAVIFORMIS. 
Pl. XXIV. rig. 1 a-k. 
Atrypa naviformis. Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 71, fig. 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 striae, 
which, on old shells, become quite conspicuous towards the margin ; young shells with the fine 
concentric and radiating striae 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 following 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 dorsal 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 f. A portion of the surface enlarged. 
Fig. 1 g, h, i, k. Several views of a young shell, the front 1 i, 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 (n. sp.). 
Pl. XXIV. Fig. 2 a - h. 
Shell elongated, cylindrical, gibbous, width 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- 
