I03 St. Maurice and CIvAibornk Pelkcypoda 103 



line of the shell varies greatl}^ as will be seen by referring to the 

 above-mentioned plate and figures. Had we Claiborne fossil- 

 iferous outcrops ranging from Texas to the Carolinas it is quite 

 possible and even probable that this species would show vari- 

 ations in shape and markings quite equal to those displaj^ed by 

 the St. Maurice and Jackson species. Were this species older 

 than, instead of younger than the St. Maurice diversified spec- 

 imens it would be easy to see how the latter could be regarded as 

 simply specialized forms, or derivatives from this, and how the 

 Jackson tj^pes are nothing but slightly modified St. Maurice 

 specimens. Here then we have the same peculiarity noted un- 

 der the rotimda stock of Venericardia, that often the St. Maur- 

 ice and Jackson forms seem very much more nearl}^ related than 

 do the Claiborne and Jackson specimens. Flexicrtis is a striking- 

 ly strong striate ludoviciamLs with perhaps texamis affinities ; 

 produdiis is directly derived from htdovicianus , and postdarkensis 

 is akin to c/arkensis, s. s. with less sinuosity along the post-basal 

 margin. From an ancestral form which seems to be carried 

 along in protextus, all these forms have descended. 



7)//>^.— Phila. Acad. Nat. Sci. 



Horizon. — Claiborne Eocene. 



Spedmens figured. — Paleont. Mus. Cornell Univ. 



Localities. — Claiborne sand, Claiborne, Ala. 



Crassatellites texaltus Harris, PI. 36. Fig. i - 3. 



Crassatella texalta Har. , Proc. Phila. Acad. Nat. Sci., 1895, p. 49, 

 pi. 2, fig. 2, 



Harris' s original description. — General form as figured ; exterior 

 smooth about the umbones, but marked by lines of growth anteriorly and 

 sub-basally ; hinge and marginal crenulation as in C. alta Con. 



This species is closely allied to C. alta, but is distinguished by its pro- 

 portionally longer form and its smooth umbones, the latter feature being 

 in marked contrast with the corrugations of C. altus. 



This is a more angular form than altus (see pi. 36, figs, i 

 and 6) when adult, and lacks the coarse umbonal undulations. It 

 is intermediate between trapaqtiara and altus. It has not the ob- 

 liquity, or the posterior, rounded fullness of obliquatus (Mon. 

 U. S. G. S. IX, 1885, p. 235, pis. 29, 30). Again, unless Whit- 



