1 052 GRANDIDIEP.TA 



A group of small Uniones, which seems to be confined to 

 Lake Tanganyika in Tropical Africa. Most of the species 

 l.ave well marked, concentric sculpture which shows a ten- 

 dency to become wavy or zigzagged, and it often becomes 

 granulous. Quite commonly the pseudocardinals are reflexed 

 and considerably ragged. The group from conchological char- 

 acters seems to be closely related to the African species, which 

 I have placed in Parreysia. 



I would not be surprised if, when the anatomy of the 

 Grandidierias is known, it may be found that all four gills of 

 the female contain embryos when gravid as, apparently, is the 

 case in Parreysia. The beak sculpture of many of the Quad- 

 rulas closely approaches that of the Bndobranchice, and there 

 may be a sort of connection between Quadrula, Physiinio, 

 Parreysia, Grandidieria and the Endobranchs in general. 



Key to speciks of Grandidieria. 



Shell nearly smooth, rayed. G. tanganyicensis. 



Shell sculptured, rayless or nearly so. 



Short elliptical, strongly sculptured. G. hurtoni. 



Ovate. 



Rather short, biangulate behind. G. graznda. 



Pointed behind. G. smitJii, rothschildi, thomsoni. 



With full beaks, much drawn out behind, G. rhynchonella. 



Narrowed and drawn out in front and behind, G. callista. 



Decidedly rhomboid. G. bourguignati. 



Grandidieria burton i (Woodward). 



Shell short, elliptical, subsolid, inequilateral, convex or sub- 

 inflated : beaks small, moderately elevated, turned forward, 

 pointed, their sculpture appearing to be very faint corruga- 

 tions ; posterior ridge low, rounded, having two feeble, raised, 

 radial ridges above it, ending in a blunt point about on the 

 median line; surface with three patterns of sculpture consist- 

 ing of irregular, concentric ridges, faint, radial impressions 

 and fine, chevron-shaped bars, which break up more or less 

 into nodules or granules ; epidermis thin, pale brownish or 



