TRIASSIC FOSSILS. 33 



dulations. Length, .3 inch from anterior to posterior extremities. 

 "Width, .28 inch. Smaller and more oblique than the preceding 

 species : the central position of the beak and the straight hinge- 

 line will serve at once to distinguish this little shell. 

 Width, .25 inch; length, .2 inch. 



Locality : El Dorado Canon, Nevada Territory, near Dayton. 



Collected by Prof. Whitney. Probably of the same age as the preceding species. 



MYOPHORIA, Bronn. 



M. alta, n. s. 



PI. 6, Fig. 33. 



Shell small, inequilateral, higher than wide, abruptly trun- 

 cated posteriorly ; anterior end and base broadly rounded ; beaks 

 central, approximate, curved anteriorly; umbonal ridge acute, 

 with a slight depression immediately in advance ; surface posterior 

 to this ridge abruptly descending to the posterior margin, and 

 with a few radiating lines ; anterior to it, the surface is marked 

 only by faint concentric lines. 



Figure, twice natural size. 



Locality: Dun Glen, Sierra District, Humboldt County, Nevada Territory. 



A single imperfect specimen, collected by Prof. Brewer, at Gifford's Ranch, 

 Plumas County, has most of the characters of this species, and is about the size of 

 the figure ; but differs in having the beak more strongly curved forwards, and in 

 the anterior margin being more prominent. These differences may be the result of 

 the difference of age in the two specimens. 



PECTEN, Linn. 



P. DBFORMIS, n. S. 

 PI. 6, Fig. 34. 



Shell small, thin, compressed, inequilateral, base oblique, ends 

 subequal ; sides sloping with a slight convexity from the apex ; 

 ears subequal, moderate in size. Surface marked by about 

 twenty-five irregular, rather large, radiating ribs, a few of which 



PAL. VOL. I. — 5 



