290 rAL.EONTOLOGY. 



nearly equally convex; liin<j;e-line equaling two-fiftlis to one-lialf the trans- 

 verse diameter of the vahcs; posterior ear very short, or nearly obsolete, 

 flat, and (il)li(|Uel\- truncated; antei-ior ear larger, flattened, and marked by 

 rather distinct lines of grow th in the right valve, separated from the adjacent 

 margin by a more or less angular sinus, one-third to one-half as deep as the 

 length of the ear, measuring from the beak. Surface stria; very fine, regu- 

 lar, sharply impressed, and increasing in number by the intercalation of 

 others between as they diverge in extending from the nmbonal region, so 

 strongly arched as to run out on the hinge-line near the beaks; concentric 

 strife fine, regular, closely arranged, and often nearly or quite obsolete on 

 the impressed spaces between the impressed radiating stri;r, to which latter 

 they impart a subpunctate appearance." 



The above is a transcript of Mr. Sleek's description of this species. 

 Although there are quite a number of specimens in the collection which are 

 referable to it, there are none which give the entire characters of the shell; 

 nor are there any from which a figure conld be made without some resto- 

 i-ation. Still the characters of the species are, nevertheless, shown so dis- 

 tinctly as to leave no douljt as to the correct reference. The specimens 

 are generally smaller than the fignres given by Mr. Meek, and some of 

 them are a little more oblique in outline, while the characters of the sur- 

 face vary from being nearly smooth to those strongly cancellated; while 

 on some the concentric striai are strongest, and on others nearly obsolete. 



Formation and locality. — Jurassic; specimens have been recognized from 

 northwest of Ra\vlings Station, Wyoming, and from Sheep Creek, and 

 Flaming Gorge, Uinta Range, Utah. Collected by S. F. Emmons, esq. 



CAMi'Tor<KCTES EXTENUATUS Meek. 



Plato VII, fig. 18. 



Cumptonectcs ? cxleiwatus Meek, Pal. Upper Missouri (Smitbsoniau Contributions to 



Knowledj^e), p. 78. 

 Cam2)((mecten ? pcrtcuuis M., ib., pi. ill, exphmations of fig. G. 



Shell small, erect, broadly ovate, a little higher than wide, the point of 

 greatest width being near the middle of the shell; hinge-line short, abont 

 half as long as the width of the valve; ears small, the anterior one slightly 



