FOSSILS OF THE POTSDAM GROUP. 207 



margin ; also two shorter, widely-diverging impressions near the beak. The 

 same features are seen in the smaller valve, except that the shorter impres- 

 sions are less divergent. 



There may be some doubt as to the true generic relations of this shell. 

 Its entire phosphatic structure places it at once among the true Linguloid 

 species, but the muscular scars are not quite like those of Lingidepis. We 

 know of no species very closely resembling it with which it may be com- 

 pared. 



Formation and locality. — In thinly laminated siliceous and somewhat 

 ferruginous shales of the Potsdam formation, in the Eureka District, 

 Nevada. Collected by J. E. Clayton, esq. 



Genus, KUTORGIN A, Billings. 



KUTOEGINA MINUTISSIMA n. Sp. 

 Plate I, figs. 11-12. 



Shell minute, quadrangular in outline, and a little wider than long, 

 with a straight hinge-line nearly or quite equaling the greatest width of the 

 shell; sides straight or slightly rounded; antero-lateral angles rounded; 

 front margin broadly rounded or very slightly emarginate in the middle by 

 the very faint mesial sinus of the dorsal valve. Ventral valve somewhat 

 pyramidal, with the side formed by the cardinal area vertical; apex of the 

 valve obtusely pointed; cardinal area triangular, about half as high as wide. 

 Features of the area and foramen not observed. Dorsal valve convex, but 

 much less elevated than the ventral, and having the beak obtusely rounded 

 and rather tumid, a very little projecting beyond the cardinal line; middle of 

 the valve marked by a very broad, shallow, and faintly-defined mesial sinus, 

 which does not extend quite to the apex of the valve. 



Surface of the shell marked by fine, elevated, concentric lines, which 

 are sharp on the top and often interrupted in their course, coalescing or bifur- 

 cating, and appearing as if broken, giving a peculiar roughened but not 

 lamellose surface-structure. There are also a few very faint, scarcely 

 defined, and somewhat irregular, distant radii. This latter feature has only 

 been observed on the dorsal valve. 



