934 PALiEONTOLOGY OF NEW-YORK. 



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. 



This species is quite rare, and the individuals figured may be only the young, 

 the mature forms having escaped observation. 



Fig. 7 a, b. Ventral and profile views of a small individual. 

 Fig. 8 a, h. Ventral and front views of a more rotund form. 



Geological position and locality. In the shaly limestone of the Lower Helderbefg 

 group : Albany county. 



Rhynclionella transversa ( n. s.). 



Plate XXXIV. Fio. 9-16. ' 



Shsll subtriangular, wider than long, tapering abruptly to the beak. 

 Ventral valve depressed convex, most prominent near the beak : beak 

 arched. Dorsal valve a little larger, most elevated near the front : beak 

 incurved ; foramen narrow, continued up to the apex of the beak. 



Surface ornamented by about fourteen or fifteen sharply elevated plica- 

 tions on each valve, of which from three to four are elevated near the 

 front into a rather faint mesial fold, and two or three depressed on the 

 ventral valve so as to form a faint sinus in the front. Somewhat strong 

 zigzag lines of growth mark the surface of the valves near the margin 

 in front. 



Fig. 9 - 14 a, h, c. A series of individuals showing a regular gradation in size, with a 

 gradually increasing depth of sinus. 



Fig. 15 & 16 a, b, c. Individuals having a more strongly defined sinus and mesial lobe ; a 

 single individual having but two folds in the sinus. 



There is usually associated with this species another which agrees very nearly 

 with it in character, being wider and more depressed in form, and which, without 

 a better series of specimens for examination, I am unwilling to regard as distinct 

 from this one. See figs. 17 - 19, same plate. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Helderberg mountains, Albany county. 



