CRETACEOUS FOSSILS. 265 



Length, .4 inch ; greatest width, 32 inch ; lesser, .24 inch. 



This species is allied to C. Mathewsonii of the California rocks, hut differs in its 

 less compressed form, the presence of hut two folds in the mouth, placed in a 

 different manner, and in the details of the sculpture. 



PHOLADOMYA, Sowb. 

 P. Sonorensis, n. s. 



PI. 36, Fig. 12. 



Shell elongate, suboval, very oblique, gibbous; beaks one- 

 fourth of tbe length from the anterior end, which slopes nearly 

 straight from the beaks to the middle, and is narrowly rounded 

 or subtruncate below ; cardinal margin concave ; base irregularly 

 convex, most prominent at, or a little posterior to the middle; 

 posterior end regularly rounded. Surface marked by numerous, 

 prominent, rounded, irregularly disposed, concentric ribs, crossed 

 by four or five faint radiations, dividing the surface into as many 

 obsolete planes. In some cases, the spaces between the radiating 

 lines are faintly concave. 



This shell is quite rare. I have seen hut two or three specimens. It is not unlike 

 P. Oregonensis, supra (PI. 29, fig. 65), but the beaks are less anterior, the cardinal 

 margin is more convex, the posterior end is more regularly rounded, and the con- 

 centric ribs are strong and prominent, instead of being nearly obsolete, as in that 

 species. 



TAPES, Megerle. 

 T. IIilgardi, Shum. 



PI. 36, Fig. 13. 



[Tapes Hilgardi, Shumard ; Trans. St. Louis Acad., 1860, p. 601.) 



The present shell agrees with Dr. Shumard's description, and with a sketch 

 which Mr. A. E. Eoessler, late assistant in the Texas Survey, was kind enough 

 to lend me, and which he made from the original type. Following Dr. Shumard, 

 I refer the species to Tapes, though the hinge is not yet known, and I am confi- 

 dent that a thorough revision will be required among the numerous species referred 

 to the various genera of Veneridce, where generic distinctions are based so exclu- 

 sively on the hinge, and where external form is of so little value. The recent 



PAL. VOL. II. — 35 



