137 St. Maurice and Claibokne Pelecypoda 137 



This shell lias the appearance of having been filled np with 

 shell matter from within, leaving the muscular scars and pallial 

 sinus very deeply sunken in the shell mass. In casts of the in- 

 terior, these features appear ver}- prominent. The greatest depth 

 of the shell is at the anterior curve or angulation of the pallial 

 sinus. The complete filling of the umbonal region with shell 

 matter is somewhat unusual. 



Variety lisbonensis (described wvi6.^x pcrovata) , if larger and 

 thicker would appear exceedingly close to this form. The out- 

 line of the shell is often verj' much like that of pearl eiisis. It is 

 difficult to say whether this species is more closel)^ related to lis- 

 bonensis or subimpressa. Some specimens could very well be re- 

 ferred to mutations of either. The pallial line is somewhat dis- 

 tant from the basal margin of the shell, reminding one of Crassi- 

 tellites ; this is especially true in the very much shortened vari- 

 eties of the species. 



Casts of this species are exceedingly abundant in the coarse 

 silicious limestone about Newbern. Occasionally other species 

 are found. At first we are astonished at the great amount of 

 variation this species shows. But, s\\\\,perovata in the Claiborne 

 shows just as much. Rarely we find pseudomorph which a.s- 

 sists greatly in determining the exterior characteristics (fig. 7, 

 a). Though the shell matter is often very thick, the diameter 

 of the valves is never proportionally so great as in typical pero- 

 vata. In fact, this seems to be a less specialized form, an over- 

 grown lisbonensis. 



Type. — Paleont. Mus. C. U. 



Horizon. — St. Maurice Eocene. 



Specimens figured. — Cornell Univ. 



Localities. — In the "Trent formation" about Newbern, N. 

 C, especially at Rocky lyanding on the Neuse above Newbern, 

 Har. Coll.; 16-17 above Newbern, Neuse River, Exp'd .'98. 



Meretrix perovata var. lisbonensis, n. var., PI. 43. Figs. 8-9. 



Varietal characterization. — General features as figured, ap- 



