76 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



convex outline above, and rounding into the base below; anterior margin 

 sinuous just under the beaks, moderately prominent near the middle, and 

 rounding into the base below: umbonal region of both valves very gibbous; 

 beaks prominent, anterior, or subterininal, pointed and incurved, with a for- 

 ward obliquity at their extremities; hinge-margin thin and apparently smooth, 

 or only very minutely crenate; surface marked by extremely fine, regular, 

 closely-arranged, radiating stria?, which appear to increase chiefly by bifurca- 

 tion, and continue of uniform size on all parts of the shell; crossing these, 

 there are less regular, more distant, small, concentric marks of growth. 



Length, measuring obliquely forward and upward from the base to the 

 beaks, 0.55 inch ; diameter, directly from the base to the hinge, at right angles 

 to the greatest length, 0.40 inch; convexity, 0.37 inch. 



This is a very neat little shell, still showing the pearly lustre of the inte- 

 rior. It is closely allied to C. sericea, Conrad (Jour. Acad. Nat. Sci. Philad., 

 new ser., IV, pi. 46), but differs in being much larger, uniformly more 

 broadly ovate in outline, and in having its beaks less elevated and not so 

 strongly incurved. If Mr. Conrad's name Stalagmium should be retained 

 for a. section of this genus, the name of this species would doubtless have to 

 be written C. {Stalagmium) elegantula. 



Locality and position. — Deer Creek, near North Platte; from the lower 

 part of the Fox Hills group of Upper Missouri Cretaceous; also on Yellow- 

 stone River, in the upper part of Fort Pierre group. 



DIM Y ARIA. 



ARCID^E. 

 Genus BARBATIA, Gray. 



Synon.— "Daphne (part), Poli (1791), Test. Utr. Sic, I, 33 (not Linn.). 



* I am uot quite sure that Poli's name Daphne, published iu 1791, may not have to be used for this 

 genus. Poli ranged but two species under it, the first of which was Area Noce, and the second A. barbaUa. 

 Those who follow the rule of always taking the first species mentioned by an author in proposing a new 

 genus, as its type, would, of course, make Daphne, Poli, an exact synonym of the older genus Area, Linn.; 

 his iirst species belonging to the latter genus. This rule, however, is by no means universally followed, 

 and could not be consistently carried out in conchology without creating great confusion among the 

 names of the older genera. If we, therefore, view Poli's first species as being reclaimed by the older 

 genus Area, his name Daphne would thus be left to stand alone for the group including his second species, 

 and, consequently, his genus would bo equivalent to the much later name Barbatia, which it may possi- 

 bly have yet to replace. It is objectionable, however, on account of being iu use by botanists for a still 

 older Linuajan genus of plants ; though naturalists most generally agree that the same generic names 

 may be used for genera in botany and zoology without creating confusion. 



