85 St. Maurice and Claiborne Pelecypoda 85 



and alticostata ; and finally, the general shortness of the shell as 

 in carsonensis2^\\di rotunda, with the ribs ornamented by the fun- 

 nel-shaped nodules so well shown in the fungina variety of ro- 

 hi7ida. 



The in-curving of the pronounced beak and the lack of de- 

 velopment in the post ero-basal region give this form a slight 

 VerticordiaASk.Q. aspect. On passing into the St. Maurice stage 

 this often becomes more quadrangular, less inflated, and above 

 all seems to lose nearly all the terrace structure of the ribs in the 

 multicostate specimens. 



Table shotvijig rotmida-alticostata relationship 

 Jackson {pmcisa tetrica carsonensis) eutawcole?is 



""[ i i 



Claiborne {^fungina rotunda funiculus') alticostata 



I I 



flabellimi coloradonis alticostata natchitoches 



St. Maurice trapaquara peraiitiqua 



coniplexicosta 



I 

 ''^alticostata f var." 



Sabine greggiana 



I 



Midway wilcoxensis 



Ill-defined and unrecognizable species of Venericardia described by 



Conrad. 



Proc. Phila. Acad. Nat. Sci., 1847, P- 297. From Eocene 

 Rocks, St. Matthew's Parish, Orangeburg District, S. C. 



Cardita carolinensis 

 Suborbicular? profoundly ventricose, with about thirty very promi- 



