﻿PEGiAS 473 



subconcentric corrus^ations, generally swollen on the posterior 

 ridge ; epidermis decorticated, but showing- a few dark, radial 

 rays on the base of the shell ; pseudocardinals rather solid : lat- 

 erals wanting. Animal having- the marsupium empty in the 

 specimen examined ; inner gills larger in front, free from the 

 abdominal sac, all four truncated behind ; palpi large ; mantle 

 with square spots on its edge ; branchial opening with a few 

 large papill?e : anal opening smooth, not separated from the 

 superanal. 



Type, Margaritana fabiila Lea. 



Pegias fabula (Lea). 



Shell oblong, subcompressed, solid, inequilateral ; beaks not 

 very full or high but pointed, sculptured with four or five very 

 strong folds, which run parallel with the growth lines or are 

 slightly oblique; posterior ridge angular, ending behind in an 

 angulation at the base of the shell ; there is another ridge on 

 the posterior slope near the dorsal line, which also ends behind 

 in an angulation ; posterior end tnmcated between these ridges 

 either squarely or obliquely ; often the upper point extends be- 

 yond the lower one ; base line generally incurved in front of the 

 posterior ridge ; epidermis decorticated, rayed below and be- 

 hind, often widely below ; left valve with an irregular triangu- 

 lar tooth under the beak, sometimes with a vestige of another 

 in front of it ; right valve with one tooth in front of the beak ; 

 laterals wanting or represented by mere blurred, faint ridges ; 

 beak cavities rather deep, compressed ; anterior muscle scars 

 impressed ; nacre whitish on the anterior border, flesh-colored 

 or salmon in the cavities, greatly and suddenly thickened in 

 front. 



Length 35, height 22, diam. T2 mm. 



Length 30, height 16, diam. ti mm. 



Cumberland and Tennessee River systems. 



Type locality, Cumberland River. Tenn. 

 Margarita fMargaritana) fahnla Lka, Syn.. 1836. p. 46; T838. 



p. 28. 



