1308 DiPLonox 



This species is evidently very closely related to D. novcc- 

 iiollaiidicc (jray, but it differs from it in being more compress- 

 ed, shorter, in having' its dorsal and ventral outlines more 

 nearly parallel, and in being covered with pustules throughout. 

 In that species the strongest sculpture is on and behind the 

 posterior ridge ; in ivebstcri the nodules of this region are faint 

 and low. .Mr. Webster, who sent me specimens, states that 

 they are not adult, but that he has one four inches in length. 



DiPi.ODON MUTABiLis (Lea). 



Shell much elongated, widest behind, subrhomboid or sub- 

 trapezoid, rather thin, compressed, inequilateral ; beaks but 

 little elevated, subcompressed, showing somewhat extended, 

 curved, subradial, slightly nodulous bars ; posterior ridge full, 

 widely rounded, ending in a blunt point at the base of the 

 shell ; base slightly incurved medially, full behind the middle ; 

 dorsal line curved : anterior end narrowed, rounded ; dorsal 

 slope obliquely truncated; surface nearly smooth, brownish- 

 olive ; teeth rather feeble ; pseudocardinals short, somewhat 

 dentilate ; laterals nearly straight ; nacre bluish, a little thicker 

 in front. 



Length 55, height 26, diam. 13 nun. 



Murray River. Australia. 

 Unio nintabiUs Lka, Pr. Ac. N. Sci. Phila., Ill, 185^, p. 152; 



Jl. Ac. N. Sci. Phila., I\', i860, p. 248, pi. xxviii, fig. 127; 



Obs., VII, i860, p. 66, pi. XXXVIII, fig. 127. 

 Margaron (Unio) mvtabilis Lea, Syn., 1870, p. 53. 

 Diplodon iniitabilis Simpson, Syn., 1900, p. 894. 



The type is not in the Lea Collection, which contains two 

 smaller shells. It is much more elongated and narrowed in 

 front than paramattnisis and the base is more nearly straight. 



Subgenus L.i^virostris Simpson, 1000. 



Lcei'irostris Simpsox. Syn., 1900, p. 894. 



Shell irregularly quadrate, thin, inequilateral, compressed, 

 rounded and narrowed in front, somewhat biangulate and trun- 

 cate behind; beaks rather low. without sculpture; surface fine- 



