1266 niPLOixjN 



Right lateral on!}- moderately curved, very slender, slightlv 

 roughened, more so on the inner than on the outer edge. Left 

 laterals thin, and lamellar, inner one larger and better devel- 

 oped than the dorsal, both with roughened edges. Nacre blu- 

 ish, with many spots of livid olive, which are more numerous 

 and extensive in the dorsal part of the shell than ventrally. 

 Posterior part iridescent. 



Leng-th 55, height 25.9, diam. 14.5 mm." (Bartsch). 



Type locality, \^ictoria Island, Lake Nahuel Huape. Argen- 

 tina. 

 Diplodon htiapensis 1 Bartsch, Pr. U. S. Nat. Mus., XXX, 



1906, p. 394, pi. XXVI!-XXIX. 



"The shell in a general way recalls Diplodon casivblanccc 

 IMiilippi and Diplodon frcnzellii Ihering. but can readily be 

 distinguished from them by its narrower outline." 



DiPi^ODON MARTENSi (von Ihering). 



Shell long rhomboid, a little wider behind, subinflated, sub- 

 solid, quite inequilateral, with low beaks whose sculpture is 

 not shown in the figure; posterior ridge low, rounded, ending 

 behind in a rounded point at the base of an oblique posterior 

 truncation and near the basal line ; base line a little incurved 

 in the middle, full behind the emargination ; surface smooth, 

 greenish-chestnut ; pseudocardinals sublamellar ; laterals re- 

 mote; nacre silvery, iridescent. 



Length 59. height 29, diam. 21 mm. 



Southern I>razil. 

 Unio martcnsi von Ihering. Arch, fiir Nat., 1893, p. 100, pi. 



TV, fig. 10. 

 Diplodon martcnsi Simpson, Syn., 1900, p. 882. 



Diplodon dunkerianus (Lea). 



Shell oblong, irregularly elliptical, a little wider behind, in- 

 equilateral, scarcely subsolid ; beaks rather low, not inflated, 

 their sculpture rather strong, sometimes corrugated, radial 

 bars, the posterior ones extending well over the disk ; j)oste- 

 rior ridge well developed, somewhat biangulate, there being 



