19 St. Maurice and Claiborne Pelecypoda 19 



superposed b}- fine secondary rays and a strong tendenc>- to have 

 the hinge line extended, giving the shell an auriculate aspect are 

 features tending to differentiate this from earlier varieties. 



X-AriQty CO nee Ulrica Dall (Trans. Wag., p. 762.) "Is marked by 

 a total disappearance of radial striae and the development of fine, 

 even, regularh^ spaced, concentric, elevated sculpture all over the 

 shell." This tends to give way to the MswsX/ilaiiientosa structure 

 when a dozen or so specimens are examined from ari\' one local- 

 it}'. (See figs. 9 and 12.) 



\r ?ir\e.\.y planata (Aid., Jr. Cin. Soc. Nat. Hist., vol. 9, 1886, 

 ]). 45, pi. 2, iig. 20) is one of the commonest forms in the St. 

 Maurice. Here the wrinkling of the concentric lines at even in- 

 tervals catising radii of various orders or dimensions, reaches the 

 limit. So important does this feature become that the original 

 concentric lines are practicalh^ obliterated and rows of scaly 

 spines, hollow and long in certain rays are the dominating feature 

 of the shell surface. See fig. 17. Large old specimens like fig. 

 16 often show clearly a tendency to become strongly plicate 

 about the basal margin. These plications are however, more nu- 

 merous than in the later Claiborne sand specimens. 



Types. — P. filamentosa (Phila. Acad.); eoncentrica (U. S. 

 Nat. Nus.) ; planata (Aid. Coll., J. H. Univ. Coll.) 



Horizon. — Uppermost Sabine to Jackson. 



Specimens fig2ired. — Cornell Univ. Paleont. Mus. 



Localities. — V^ox filamentosa, sen. str., Claiborne sands ; for 

 concentirca, pre-eminently the Texas variet}^ common in Cher- 

 okee, Anderson, Houston and Robertson Co's ; Columbus and 

 Negreet, Sabine Pam., La., Wautubbee, Miss. ; for planata, 

 Newton, Hickory, Wautubbee, PI. Johnson's, Miss, and St. 

 Maurice, Cooper's Well, Winnfield, about 1000 ft.. La. 



Pecten deshayesii PI. 13- Figs. 2-7. 



P. deshayesii Lea, Cont. to Geol., 1833, p. 87, pi. 3, fig. 66. 



P. lyelli heaid. p, 87, pi. 3, fig. 67. 



P. deslmyesii de Greg., Mon. Faun. Eoc, 1890, p. 180, pi. 21, figs. 



12-15. 

 Lea's original description. — vShell orbicular, rather compressed ; ears 



