852 PROCEEDINGS OF THE NATIONAL MUSEVM. vol.xxii. 



end of the ligament parallel with the base, behind the ligament the 

 shell is obliquely truncate, the trancatiou somewhat upcurved, the 

 shell ending in a rounded point at the posterior basej i:)osterior ridge 

 elevated, rounded, with sculpture radiating from it above and below; 

 beaks rather low, radially ridged ; pseudocardinals small, generally two 

 in each valve; laterals rather short, club-shaped, one in the right and 

 two in the left valve. Animal unknown. 



(Group of Virgus heccariamis.) 



Shell having the posterior ridge high and rounded, outlined on each 

 side by a sulcus, the radiations from this ridge rather fine; surface 

 concentrically sculptured. 



VIRGUS BECCARIANUS Tapperone Canefri. 



'^Unio beccarianus Tapperone Canefri, Add. Mus. Genov., XIX, 1883, p. 291, pi. 

 XI, fig. 2.— *P.ETEL, Conch. Sam., Ill, 1890, p. 145. 



Fly Eiver, New Guinea. 



(Group of Virgus mattiroli.) 



Posterior ridge full, rounded, not outlined by sulci, covered with 

 very strong corrugated ridges which curve outward each way from the 

 center, the remainder of the shell smooth. 



VIRGUS MATTIROLI Tapperone Canefri. 



* Unio mattiroli Tapperone Canefri, Auu. Mas. Genov., XIX, 1883, p. 292, pi. 



XI, iig. 1.— *P.etel, Conch. Sam., Ill, 1890, p. 158. 



Fly Eiver, New Guinea. 



(Group of Virgus misoolensis.) 



Posterior ridge merely rounded, with radiating folds scattered over 

 the shell, pseudocardinals two in the left valve and one in the right. 



VIRGUS MISOOLENSIS Schepman. 



* Unio misoolensis Schepman, Notes from Leyd. Mus., XVIII, 1896, p. 259, iig. — 



"Drouet, Jl. de Couch., XLV, 1897, p. 125. 



Misool, Borneo. 



Genus CTENODESIMA Simpson, 1900. 

 (Type, Unio horneensis Issei. ) 



Shell subtrapezoid to long elliptical, rather thin, compressed, with a 

 scarcely developed posterior ridge and low beaks whose sculpture is 

 densely zigzag radial, becoming finely corrugated or nodulous on the 

 disk and extending over most of the shell; the disk concentrically 

 striate or sulcate at its outer edge; pseudocardinals one to two in each 

 valve, very diverse in form, but showing a tendency to break up into 



