206 PALJSOI^JTOLOGY. 



Genus LINGULEPIS Hall. 



. LiNGULEPIS M^RA D. Sp. 

 Plate I, figs. 5-7. 



Shell small, sliort-ovate, a little longer than wide, point of greatest 

 width a little below the middle of the length; base regularly rounded; beak 

 small, pointed, and slightly incurved; cardinal slopes long, diverging from the 

 beak to below the middle of the shell, and inclosing an angle of about ninety 

 degrees. Valves convex, a little the most ventricose above the middle of the 

 valve; the beak of the longer valve appearing quite full and round. 



Surface of the shell apparently smooth. Internal cast distinctly 

 radiated. 



The surfaces of the shells are all more or less exfoliated in separating 

 from the matrix, and in this condition are more or less lamellose in their 

 structure, while the layers are bright and polished. The shell in many of 

 its features resembles L. pinnaformis Owen, from the Potsdam sandstones 

 of the St. Croix River, but has not the extended beak of that species, the 

 valves being more nearly of equal length, that of the ventral exceeding the 

 dorsal only by the beak being pointed instead of rounded. 



Formation and locality. — In hard, somewhat ferruginous, sandy limestone 

 of the Potsdam group in the Eureka District, Nevada. Collected by Arnold 

 Hague, esq. 



LiNGULEPIS ? MINUTA D. Sp. 

 Plate I, figs. 3-4. 



Shell minute, seldom exceeding a line in its greatest diameter; in form 

 very short-ovate, the greatest width considerably below the middle of the 

 length and narrowing to the beak, especially on the larger valve, which is 

 apparently slightly truncate at the extremity; base broadly rounded. 

 Valves moderately convex, but not rotund. Smaller valve nearly circular. 

 Substance of the shell nacreous and apparently phosphatic, not presenting 

 any appearance of having been calcareous; the exterior concentrically 

 lamellose. 



Casts of the interior of the larger valve show a sharp, longitudinal 

 depression along the middle, extending in some cases to near the front 



