ortmann: south American naiades. 



629 



Simpson's measurements do not agree with these figures. 



It should be noticed that young specimens are not so liigh, and also less swollen 

 than older individuals, and thus the typical shape is less evident in them. They 

 are also extremely thin-shelled, while older ones are rather solid. 



Anatomy. — I have nine males and five females. The structure is exactly like 

 that of A. riograndensis. The iialjM have their i)ostcrior bases separated; for 

 about two-thirds of their length the bases are contiguous, but then they diverge. 

 The inner gill begins just without and close to the end of the inner palpus. 



64. Anodontites rioplatensis (Sowerby) (1870). 

 Anodon rioplatensis Sowerby, XVH, 1S70, PI. 26, fig. 101. 

 Glabaris trapesialis rioplatensis Simpson, 1900, p. 925. 

 Anodontites trapesialis rioplatensis Simpson, 1914, p. 1431. 



Type-locality. — Rio de la Plata. 



Other Localities. — Haas (1916, pp. 29, 54) mentions a closely related form from 

 Rio Uruguay, Salto Oriental, Uruguay, which may, or may not, be this. 



New Locality. — Rio Limay, Patagonia, Argentina (received in exchange from 

 W. Israel). One specimen. 



Distribution. — The Rio de la Plata and Rio Negro drainages in Argentina. 

 Possibly also in Rio Uruguay. 



We may regard this as an exaggerated forbesiana, with the shell higher and 

 shorter, and the beaks more central, but in all other respects it is similar. Sow-erby 

 calls the shell thin, and describes concentric "wrinkles" on the beaks. Our speci- 

 men is rather solid, and the wrinkles are nothing but growth-lines. 



Subgenus Lamproscapha Swainson (1840). 

 Lamproscapha Swainson, Treat, on Malacology, 1840, p. 381. 

 Virgvla Simpson, 1900, p. 931; 1914, p. 1454. 



Shell greatly elongated, knife-shaped, sharply })ointed behind, with a sharp 

 posterior ridge. Posterior retractor-sear completely separated from the adductor- 

 scar, and remote from it by about one to three times its own diameter. Epidermis 

 not shining, covered with very fine concentric (posteriorly) and radial scalari- 

 form (anteriorly) wrinkles. 



