DESCRIPTIONS OF NEW SPECIES. J 13 



small; scar of attachment usually small and sometimes absent; surface com- 

 paratively smooth for an oyster ; a few faint radiating plications appearing 

 upon some examples. Length of largest example nearly five and a half 

 centimeters ; breadth twenty-nine millimeters. 



Position and locality. Point of Rocks Group; two miles west of Point 

 of Rocks, Wyoming. 



Genus PLICATULA Lamarck. 



Plicatida liydrotlieca (sp. nov.). Shell of ordinary size, irregularly sub- 

 ovate in marginal outline; beaks rather narrow ; lower valve broadly con- 

 vex ; hinge teeth well developed ; upper valve nearly flat, or slightly 

 concave near the beak. 



Surface of both valves marked by small, slightly raised radiating 

 plications, which are crenulated, a little irregular and more or less distinct 

 upon all parts of the surface of both valves. 



Length, three centimeters ; greatest breath, twenty-four millimeters. 



Position and locality. Henry's Fork Group; head of Water-pocket 

 Canon, Southern Utah. 



Genus INOCERAMUS Sowerby. 



Inoceramus Gilberti (sp. nov.). Shell irregularly suboval in marginal 

 outline, the transverse diameter being greater than the vertical; front flat- 

 tened; valves nearly or quite equal, both being gibbous and sometimes quite 

 ventricose; umbones broad and elevated; beaks very near the front, incurved 

 but not projecting beyond the front margin ; front nearly straight vertically, 

 and forming nearly a right angle with the hinge; front margin rounded 

 below to the basal margin, which is broadly convex for more than half the 

 length of the shell; postero-basal margin extending obliquely upward, with 

 a slight emargination to the posterior extremity, which is abruptly rounded 

 to meet the downward-sloping postero-dorsal margin; dorsal margin straight, 

 its length equaling more than half the long diameter of the shell. 



Upon each valve there is an obscure radiating shallow furrow or de- 

 pression extending from the umbonal region to the postero'-basal border and 



ending at the emargination there, before mentioned. 

 SPG 



