P.\RRKYSIA I 131 



Unio fahagina Deshayrs, Nouv. Arch, de Mus., X, 1874, p. 



128, pi. VII, figs. 4-6. 

 Parreysia fahagina Simpson, Syn., 1900, p. 847. 

 UnioneUa fahagina Haas, Conch. Cab., Ilnio, 1912, pi. 31, fig. 8, 



An exceedingly solid, small species with strongly arched 

 dorsal outline, higli. sharp posterior ridge and curved laterals. 



Haas has recently, (Nachr. Deutsch. Mai. Ges., 1913, p. 

 37), made this species the type of a new genus, UnioneUa. 



Parreysia broti (Deshayes). 



Shell small, solid, inflated, rhomboid, inequilateral; beaks 

 full and high ; below them there are three strong, low V-shaped 

 ridges, and on the dorsal slope there are oblique wrinkles ; 

 posterior ridge high and decidedly angled, slightly arched; 

 anterior end narrow, rounded ; dorsal outline strongly arched 

 from the anterior end to the point at the posterior base; base 

 line nearly straight ; epidermis yellowish-green, darker on the 

 ridges and border ; pseudocardinals solid ; laterals heavy, but 

 slightly curved ; muscle scars small, deep ; nacre silvery. 



Length 15, height 11, diam. 9 mm. 



Mekong River, Cambodia. 

 Unio broti Deshayes, Nouv. Arch, de Mus., X, 1874, p. 129, 



pi. VII, fi.gs. 1-3. 

 Parreysia hroti Simpson, Syn., 1900, p. 847. 

 UnioneUa broti Haas, Conch. Cab., Unio, 1912, pi. 31, fig. 9. 

 If the specimen, which Deshayes has described, is adult 

 this is probably the smallest Naiad known. It is characterized 

 by the three very strong V-shaped bars across the disk ; it has 

 shorter, heavier, less curved laterals than fahagina. 



Group of Parreysia nyassaensis. 



Shell small, solid, inflated, triangular to rhomboid, the base 

 straight or even a little arcuate, but sometimes having a slight 

 fullness behind the central part, a high, well-defined posterior 

 ridge ends at the post-base and is sometimes slightly double ; 

 posterior slope abrupt; beaks high, with zigzag-radial sculp- 

 ture, the bars approaching and often coalescing behind the cen- 



