268 PALAEONTOLOGY OF CALIFORNIA. 



species, I find a great difference in the convexity ; that form having a far greater 

 transverse diameter. I have never been so fortunate as to see a good example of 

 the Texan shell ; and have been obliged to rely on the descriptions and figures in 

 Marcy's and Emory's Reports, almost entirely. It is not impossible that the two 

 species may prove identical, though I hardly think it possible that, had it existed, 

 so marked a character as the granules on the ribs would have been overlooked by 

 two such students as Conrad and Shumard. 



CARDITA, Brug. 



?C. ALTICOSTA, U. 8. 

 PI. 36, Fig. 16. 



SHELL oblique, subtrigonal, gibbous; beaks prominent, subter- 

 minal; anterior end deeply excavated under the beaks, broadly 

 and prominently rounded below; cardinal margin rapidly sloping, 

 nearly straight; posterior end narrow, rounded; base regularly 

 convex. Surface marked by about twenty-five high, narrow ribs 

 with concave interspaces. In some cases these ribs are smooth, 

 in others they are crossed by lines of growth, developed into 

 imbricating plates. Lunule small, broad, cordate. 



Length, .8 to .9 inch. 



Common. Although I have been unable to expose the hinge of this shell, I 

 have very little doubt of the correctness of the generic reference. Externally it 

 possesses every character of Cardita. The shell is invariably crystalline, and the 

 matrix is a tough amorphous limestone, which never yields under the chisel until 

 the shell is completely shattered J I have, in consequence, been obliged to trust to 

 external resemblances, rather than to the more certain evidence furnished by the 

 internal characters. 



PINNA, Linn. 



P. SP. INDEX. 



Fragments of a long slender Pinna are not rare in the collection. They indicate 

 a species not unlike P. Brewerii nob., but are in too fragmentary a condition to 

 warrant description. 



