40 



Bryant Wai,kf;k 



Key to the subgenera of Margaritana. 



Gills with scattered interlamellar connections forming irregular 



rows running obliquely forwards Margaritana s. s. 



Gills with continuous septa running obliquely forwards. .Cumberlandia. 



Subgenus MARGARITANA s. s. 

 Shell as in the genus. 



Fig. 140 



Animal as in the family, but having the gills without water-tubes and 

 with scattered interlamellar connections which in certain places form irreg- 

 ular rows, running obliquely forwards. 



ibr 



Fig. 141* 

 Type: Mya margaritifera h., fig. 140. Animal, fig. 141. 



*The following lettering applies to all the figures of the animals of the Margar- 

 itanidae and Unionidse except as otherwise stated : 



an. — anal opening. 



br. — branchial opening. 



f. — flaps of margin of mantle. 



i. — inner gill. 



o. — outer gill. 



p. — foot. 



pp. — papillae on margin of mantle. 



sa. — supr^-anal opening. 



mp. — marsupium. 



