REPOKT (Xtf PAL^ONTOLOGICAL COLLECTIONS. 349 



mesial sinus in the ventral valve, which sinus is also hounded by more angular and more 

 diverging ridges than we usually see in C. VernvuUiana. Our Ttah shell also seems 

 to be more extended on the hinge-line, and has more sinuous lateral margins. Its 

 striae are exceedingly fine, closely arranged, and appear to increase both by intercala- 

 tion and division. None of the specimens collected show very clearly the number ot 

 spines on the hinge-margin, though there appear to be about five on each side of the 

 beak. No specimens of the dorsal valve were obtained. 1 am inclined to think it 

 will be found specifically distinct from C. Vcrneuiliaua. 



Length of hinge, 0.45 inch; diameter from hinge to front, 0.22 inch; convexity of 

 ventral valve, 0.12 inch. 



Locality and position. — Near Humboldt Mountains, latitude 39° 57', longitude 

 115° 10'. 



Genus PKODUCTUS, Sowerby. 



Peoductus semistriatus, Meek. 



Shell of medium size, greatest breadth on the hinge-line, which is nearly twice 

 the length, measuring from the hinge to the anterior curve. Dorsal valve unknown- 

 Ventral valve very gibbous, extremely arched, and greatly produced in trout; some- 

 times provided with an obscure, very shallow mesial sinus, which never extends to 

 the beak ; ears triangular, strongly vaulted, extended nearly at right angles to the 

 vertical sides of the elevated visceral arch, from which they are each separated by an 

 oblique, undefined sulcus; beak very convex, distinctly incurved, and extended a little 

 beyond the hinge ; surface of the visceral region marked by small, obscure concentric 

 wrinkles, which are crossed by numerous, more or less bifurcating strise ; anterior 

 half smooth, or only marked by fine lines of growth ; spines rather long, erect, and 

 scattering. 



Length of hinge, 1.19 inches; diameter from hinge to anterior curve, 0.72 inch; 

 length from the beak to the anterior margin of the ventral valve, measuring over its 

 curve, 2.14 inches. 



The concentric wrinkles are most distinct on the lateral slopes of the visceral 

 arch, and seem to extend upon the ears. When the radiating strise are well denned, 

 they form, with these wrinkles, a more or less distinct reticulate style of ornamenta- 

 tion, over the visceral half of the shell. The radiating striae are generally rather ob- 

 scure, and number about ten in the space of 0.30 inch. 



This species belongs to the group Semiretkulati of Koninck ; its most marked 

 peculiarities are its narrow, strongly arcuate form, produced anterior, and the entire 

 absence of radiating strise over the whole of the ventral valve, excepting the visceral 

 half. These characters will serve to distinguish it from all the other forms resembling 

 it in other respects, yet known to the writer. 



Locality and position.— Timpanogos Canon, latitude 40° 22', longitude 111° 38'; 

 in a dark, argillaceous rock, probably of the age of the Coal-Measures. 



