290 PALEONTOLOGY. 



nearly equally convex; hinge-line equaling- two-fifths to one-half the trans- 

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

 flat, and obliquely truncated; anterior ear larger, flattened, and marked by 

 rather distinct lines of growth 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 striae very fine, regu- 

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

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

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

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

 the impressed spaces between the impressed radiating strise, to which latter 

 they impart a subpunctate appearance." 



The above is a transcript of Mr. Meek'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 could be made without some resto- 

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

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

 are generally smaller than the figures 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 strise are strongest, and on others nearly obsolete. 



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

 northwest of Rawlings Station, Wyoming, and from Sheep Creek, and 

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



Camptonectes extenuatus Meek. 



Plate VII, fig. 18, 



Camptonectes? extenuatvs Meek, Pal. Upper Missouri (Smithsonian Contributions to 



Knowledge), p. 78. 

 Camptonectes ? pertenuis M., ib., pi. iii, explanations of fig. 6. 



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, about 

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



