14 AMERICAN JOURNAL 



nearly central, cardinal margin not so long as the width of the 

 shell, straight for a short distance both sides of the beaks, then 

 bending down with a regular curve posteriorly, sub-angulated 

 anteriorly ; base narrowly rounded, most prominent directly 

 opposite the posterior end of the cardinal line ; anterior end, 

 with a portion of the base, forming about a third of a circle ; 

 posterior end less convex. Surface marked by irregular and 

 not very prominent concentric lines and undulations. 



Length, 1-45 in. ; width, 1*5 in. 



Locality. Found by Dr. A. Blatchley in the Trias at New 

 Pass, west of Austin, associated with many species, character- 

 istic of the St. Cassian group of Europe. 



It is most nearly allied to P. Bi'onnii, Goldf., but is more 

 regularly rounded in outline, and wants the angle at the 

 posterior end of the cardinal line. The surface ribs are also 

 less strongly marked than in that species. 



PINNA, Linn. 

 P. . sp. indet. 



Two fragments of a Pinna were obtained by Prof. Whitney, 

 at Mormon Station, Plumas Co., Cal., in the semi-metamor- 

 phosed sandstones of the Jurassic. They are long, slender, 

 and are marked very much in the some manner as P. Breiveriiy 

 nob., of the California cretaceous. Both specimens have suffered 

 some distortion, and, until better material shall have been ob- 

 tained, I do not feel warranted in giving a detailed description. 



CASSIaJnELLA, Beyiich. 



C. LINGULATA, Gabb.— PI. ^ fig. 13, 13a, 13b. 



Shell very thick, long, narrow, linguieform. Large valve, 

 very convex and ponderous, nearly as high as wide ; beak placed 

 in the middle, prominent, strongly incurved, umbone high, 

 rounded ; posterior ear straight, slightly sloping, sub-acuminate, 

 lateral margin slightly concave ; anterior ear more elevated than 

 the posterior, separated from the body by a marked groove, top 

 convexly sloping, lateral margin nearly straight ; below the ears 

 the sides are nearly parallel for a short distance, curving into a 

 broadly rounded base. Hinge line broad, widely open, areas 

 of both valves wide, that of the smaller valve triangular notched 

 opposite the beak of the opposite side. Small valve thin, 

 broadly concave, divided by two radiating ridges into three 

 unequal concave surfaces ; outlines corresponding with those of 

 the opposite valve, where in contact. Surface of both valves 



