96 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. 106. 



end. Surface ornamented with faint lines of growth and very obscure, 



distant, radiating lines that are preserved only on the anterior? portion. 



Length, 15 mm ; height, 6 mm 5 greatest convexity of single valve, about 



Oram 

 w . 



The type is a single valve, retaining only a portion of the shell. As 

 neither the hinge nor the pallial line has been seen, its generic refer- 

 ence is only provisional. 



Locality and position. — In the Pugnellus sandstone, Poison canyon, 

 Huerfano park, Colorado. 



CRASSATELLID^E. 



Genus CEASSATELLA Lamarck. 



Crassatella excavata n. sp. 



PL xxi, Figs. 10-13. 



Shell small, depressed subquadrate in outline; dorsal margin nearly 

 straight, declining slightly from the beak to the posterior end, which 

 is truncate almost vertically; front slightly concave above for over half 

 the distance from the beak to the basg and regularly curved below ; 

 ventral margin forming a broadly ovate curve; lunule broadly lanceo- 

 late and very deep ; escutcheon long and well denned, but not nearly so 

 deep as the lunule; beaks near the anterior end, small, pointed, approx- 

 imate, and directed forward. Posterior to the umbonal slope, which is 

 broadly rounded and not very well defined, the shell is compressed. 

 Surface marked by fine lines of growth and by narrow, subequal, some- 

 what irregularly arranged, concentric ridges. 



The hinge has the structure characteristic of the genus and the free 

 margin of the shell is crenate. Eepresented by three well preserved 

 valves. 



Length, 16 mm ; height, 15 ram ; convexity of one valve, 4 ram . 



The most nearly related species with which I am acquainted is Cras- 

 satella cimarronensis White, which has nearly the same outline when 

 viewed from the side, but it differs from the present one in its greater 

 convexity, larger size, and in the character of its surface. Its lunule 

 is proportionally much more shallow and its hinge is broader and 

 stronger. 



Locality and position. — From concretions in the Fort Benton shales 

 on Williams creek, Huerfano park, Colorado. 



RUDIST^E. 



Genus EADIOLITES Lamarck. 



Eadiolites ? 



A single fragment of a large species of Eadiolites , or Sphwrulites has 

 been collected by Mr. Edwin Blackburn in the Niobrara limestone at 

 Morrison, near Denver, Colorado, and I have seen a similar specimen, 



