74 [ Senatk 



so as to produce a faint sinus, which extends about two-thirds 

 of the way to the beak, at which point the valve is most convex : 

 the two plications bordering the sinus are larger and more pro- 

 minent than those on each side of them, and become obsolete 

 before reaching the beak. A few faint imbricating lines of growth 

 are visible near the junction of the valves in front. 

 Geological position and locality. Shaly limestone of the Lower Hel- 

 derberg group, Albany county. 



Ehynchonella inutilis. 



Pal. N.Y. Vol. iii, pi. 34, f. 7 & 8. 



Shell subtriangular, subglobose; beak of ventral valve small, 

 closely curved upon the opposite : dorsal valve a little larger ; 

 beak incurved. Surface ornamented by eighteen or nineteen 

 simple sharply elevated plications, about four or five of which 

 are elevated on the dorsal valve so as to form a more or less 

 distinct mesial fold, which extends to about the middle of the 

 valve ; while three or four of those on the middle of the ventral 

 valve are depressed towards the front into a sinus, which is faint 

 and broad in some specimens, and narrow and more distinctly 

 defined in others. A few strong imbricating zigzag lines of 

 growth near the margins of the valves. 

 Geological position and locality. Shaly limestone of the Lower Hel- 



derberg group, Albany county. 



Rhynchonella transversa. 



Pal. N.Y. Vol. iii, pi. 34, f . 9 - 14. 



Shell subtriangular, wider than long, tapering abruptly to the 

 beak : ventral valve depressed-convex, most prominent near the 

 the beak ; beak arched : dorsal valve a little larger, most ele- 

 vated near the front ; beak incurved ; foramen narrow, continued 

 up to the apex of the beak. Surface ornamented by about four- 

 teen or fifteen sharply elevated plications on each valve, of 



