RFXTTDENS I 157 



Unio bcanforti Bavay. Nova Guinea, 1908, p. 291. pi. xiv, 



fig. lO. 



"This species is very near to U. §:;uppyi E. Smith of Short- 

 land Island, Solomon Group, which itself resembles many 

 forms from Australia and New Zealand." 



Genus RECTIDENS Simpson, 1900. 



Rectideiis Simpson, Syn., 1900, p. 853. 



Shell elongated, with an angle at the anterior dorsal part, 

 pointed and slightly biangnlate behind, moderately solid, with 

 two or three posterior ridges, the lower the higher ; beaks full, 

 sculpture not observed, but probably zigzag-radial ; the pos- 

 terior slope, and often part of the disk, covered with faint, 

 granular, radiating sculpture ; epidermis smooth, olive ; one 

 compressed, short, recurved pseudocardinal in the left valve 

 under the beak, and a very long one in front of it, and two 

 laterals ; two compressed pseudocardinals in the right valve, 

 and a single lateral ; all the teeth straight or nearly so ; anterior 

 muscle scars separate ; beak cavities rather shallow ; only one 

 or two dorsal scars in each valve ; nacre white or reddish. 



Animal unknown. 



Type, Unio prolongatus Drouet. 



The species placed in this group seems to be closely allied 

 and are characterized by much elongated shells with rather 

 low beaks and delicate, lamellar pseudocardinals and laterals, 

 which are granular or more or less vertically striate. There is 

 generally a feebly double posterior ridge, each part being 

 pinched up in the upper part. All the species seem to have 

 traces of radical sculpture. 



KXY TO SPKCIES OF ReCTIDUNS. 



Shell inflated, strongly concentrically sculptured, 



R. pcrakensis. 

 Shell compressed to convex, not strongly concentrically 

 sculptured. 



