40 



Bryant Wai,kkk 



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 ior\va.rds. .Ciiinberla}idia. 



Subgenus AIARGARITANA 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 uiargaritifera L., fig. 140. Animal, fig. 141. 



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

 itanid?e and Unionida; 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. — supra-anal opening. 



mp. — marsupium. 



