19 St. Maurice and Claibornk Pe;i.kcypoda 19 



superposed by fine secondary rays and a strong tendency to have 

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

 features tending to differentiate this from earlier varieties. 



N 2x\&\.j concentrica Dall (Trans. Wag., p. 762.) "Is marked by 

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

 even, regularly spaced, concentric, elevated sculpture all over the 

 shell." This tends to give way to the nsualjilamentosa structure 

 when a dozen or so specimens are examined from an}^ one local- 

 ity. (See figs. 9 and 12.) 



YaxioXy plana ta (Aid., Jr. Cin. Soc. Nat. Hist., vol. 9, 1886, 

 p. 45, pi. 2, fig. 20) is one of the commonest forms in the St. 

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

 tervals causing radii of various orders or dimensions, reaches the 

 limit. So important does this feature become that the original 

 concentric lines are practically obliterated- and rows of scaly 

 spines, hollow and long in certain raj^s are the dominating feature 

 of the shell surface. See fig. 17. I^arge 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. Jilamentosa (Phila. Acad.); concentrica (U. S. 

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



Horizon. — Uppermost Sabine to Jackson. 



Specimens figured. — Cornell Univ. Paleont. Mus. 



Localities. — Vox filamentosa, sen. sir., Claiborne sands ; for 

 concentirca, pre-eminently the Texas variety, common in Cher- 

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

 Negreet, Sabine Pam., I^a., Wautubbee, Miss. ; for planata, 

 Newton, Hickorj^ Wautubbee, H. Johnson's, Miss, and St. 

 Maurice, Cooper's Well, Winnfield, about 1000 ft., I^a. 



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



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

 P. lyelli Lie&id. p, 87, pi. 3, fig. 67. 



P. des/tayesii de Greg. , Mon. Faun. Eoc, 1890, p. 180, pi. 21, figs. 

 12-15. 



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



