208 PALyEONTOLOGY. 



The shells have all the generic featui'es of the specimens upon which 

 the genus Ktitorgina, as given by Mr. Billings (Pal. Foss. Canada, vol. 1, p. 

 8, figs. 8 and 10; the specimen fig. 9 probably belongs to some other genus), 

 was founded, but differs specially in the minute size of the shell. Our 

 specimens figured measure scarcely a line in width, and are less in length; 

 while the original of his species, which we had the pleasure of examining 

 some years ago, considerably exceed half an inch in length. The peculiar 

 surface-character is one that cannot be easily mistaken, and one which we 

 do not remember to have seen on any other Brachiopodous shell. 



Formation mid locality. — In limestone of the Potsdam group, at Eui-eka, 

 Nevada. There are also remains of shells of the same genus, but of a 

 species two or three times the size of this one, in come green shales from 

 East Canon, Oquirrh Mountains, Utah. Collected by J. E. Clayton, esq. 



Genus LEPT.ENA Dalman. 



LEPTiKNA MeLITA U. Sp. 



Plate I, tigs. 13-11. 



Shell of medium size, transversely semi-oval in form, the length equal to 

 about two-thirds of the width; hinge-line straight, as long as the width of the 

 shell below; sides nearly straight for a short distance below the cardinal 

 extremities and rectangular to the hinge-line; lower lateral margins rounded; 

 basal line regularly convex; ventral valve depressed-convex, regularly 

 arching from beak to base, but sometimes slightly marked by a broad, 

 shallow, not distinctly defined, mesial depression ; beak low and inconspicu- 

 ous; dorsal valve concave, nearly conforming to the curvature of the opjio- 

 site valve, leaving but a limited space between the two. Area not definitely 

 ascertained, but apparently quite narrow and linear. 



Surface of the shell marked by distinct, strong, somewhat arching, 

 radiating stria?,, with an indefinite number of very fine intermediate ones 

 occupying the concave spaces between the stronger, and with them forming 

 fascicles. This feature varies very greatly in strength and number of the 

 finer stria; in different individuals, and also in the number of stronger radii; 

 in some cases there being only nine or ten of the strong radii on the entire 



