PyXRRKYSlA I I 25 



I. have never seen this shell, which seems from the descrip- 

 tion and figures to be rather closely related to the species of the 

 group of P. hakeri. It is less inflated and does not have a 

 strong posterior ridge, but the zigzag sculpture, ending con- 

 siderably above the base of the shell, is like that of the species 

 I have placed in that group. 



Group of Parrcysia hakeri. 



Shell small, inflated, oval, rounded in front, bluntly pointed 

 behind, inflated at or behind the central base ; beaks full, high, 

 sculptured with very strong, zigzag bars, which extend part 

 way over the disk and end rather suddenly, below which the 

 shell is smooth ; posterior ridge well developed, rounded : two 

 compressed pseudocardinals and one lateral in the right valve, 

 two pseudocardinals and two laterals in the left valve. 



Parreysia bakeri (H. .\dams). 



Shell transverse ovate, thin, subinflated, inequilateral : an- 

 terior end rounded ; posterior end dilated, subangulate, strong- 

 ly, undulately plicate ; epidermis olivaceous ; beaks subpromi- 

 nent, nodulous at the apices ; pseudocardinals small, sulcate ; 

 laterals nearly straight, double in the left valve ; nacre pearly 

 or silvery, iridescent. 



Length 30, height 21, diam. 14 mm. 



Lake Albert Nyanza, Central Africa. 

 Unio hakeri H. Adams, Pr. Zool. Soc. Lond., t866, p. 376. — 



Smith, Ann. and Mag., X, 1892, p. 126, pi. xii, fig. 11.— 



VON Martins, Besch. Dents. Ost-Af., 1897, p. 231, pi. vii, 



fig. 6. 

 Parrcysia hakeri Simpson, Syn., 1900, p. 846. 



Adams does not figure his species, but Smith and von Mar- 

 tens do. The figure given by the former is of a young shell 

 in the first or strongly zizzag radial stage of growth and shows 

 an obovate specimen. That of von Martens is taken from 

 an adult specimen and shows both the earlier zigzag-radial 

 and later the nearly smooth, concentric sculpture character- 

 istic of this group. His figure shows a somewhat rhomboid 



