46 PAL/EONTOLOGY OF NEW-YORK. 



At the tiino of describing this species, I had no authentic specimens of Orthis 

 lenticuiaris ; nor was I aware of the variety of forms which I have since obtained 

 and examined, and referred to that species. 



The Orthis solitaria is probably only a variety of form, or rather a greater 

 extreme of the subquadrate forms figured on Plate V of this volume. With a 

 single individual for examination (no other of the same having been obtained), 

 there may remain some doubt as to the positive identity ; and I have therefore 

 permitted the description to remain, the plate having been engraved before those 

 forms of 0. lenticuiaris were collected. 



Geological formation and locality. In the shales of the Hamilton group : at York, 

 Livingston county, N.Y. 



Orthis lepidus. 



PLATE VI. 

 OrlhiM lepidut : Hali, Thirteenth Report on the State Cabinet, 1860, p. 78. 



Shell small, transversely subelliptical, somewhat ventricose : cardinal 

 line little less than the greatest width of the shell ; area proportional- 

 ly large ; beaks distant. Ventral valve very convex, regularly curved 

 from beak to base : ventral beak prominent, pointed and slightly in- 

 clined. Dorsal valve depressed-convex, marked by a distinct mesial 

 depression, which, in some specimens, extends nearly to the beak : 

 dorsal beak small, pointed, but little incurV^ed. 



Surface marked by fine radiating striae, which are crossed by concentric 



striae and a few stronger lines of growth. 



This is the smallest species of Orthis yet known in the Hamilton group, and 



is easily distinguished by the great transverse diameter, the large area, the 



prominent ventral beak, and the distinct dorsal sinus. It is of the type of the 



preceding species, but differs in its greater width, more elevated ventral beak, 



and larger area. The specimens observed do not exceed a quarter of an inch in 



width. 



The species bears some resemblance to the young of 0. perelegans; but the 



beak is more elevated, and the area larger. It is an extremely rare form, having 



been found in but a single locality and in few individuals. 



Geologial formation and locality. In the shales of the Hamilton group, on the 



shore of Canandaigua lake, Ontario county, N.Y. 



