ortmann: south American naiades. 565 



are slightly broken off, and also in the two others they are not finite perfect. The 

 length from tip to tip of the wings is most nearly parallel to the hinge-line. The 

 height is measured vertically to the hinge-line, from the beaks to the lower margin. 



40. Prisodon castelnaudi (Hupe) (1857). 

 Hyria castelnaudi Hupe, 1857, ]). 81, PI. IG. fig. 1; Sowerby, XVII, 1SG9. PI. 4, 



fig. 8. 

 Prisodon castelnaudi Simpson, 1900, p. 871; 1914, p. 1220. 

 Prisodon obliquus castelnaudi Von Ihering, 1910, p. 135, 137. 



Type-locality. — Brazil . 



Other Localities. — Rio Araguaj'a, Goyaz, Brazil (Von Ihering); Rio Chingu, 

 Para, Brazil (Von Ihering). 



New Locality.— Rio Guapore, near Rio Sao Simao, Matto Grosso, Brazil 

 (J. D. Haseman coll., July 20, 1909). One young male with soft parts. 



In addition, there is in the Carnegie Museum one larger specimen from the 

 Hartman collection, labelled "River Amazon." 



Distrihution. — Positively known from the Amazon, two of the tributaries of 

 its lower part in Goyaz and Para, and from a tributary of the IMadeira in Matto 

 Grosso. 



My specimens agree well with the account given by Simpson, but I should say 

 that the hinge-teeth are not vertically ridged. The posterior pseudocardinal in 

 either valve is cut up by deep fissures into accessory teeth, which are somewhat 

 radiating. The lateral teeth are slightly rugose. 



Von Ihering regards this as a variety of P. obliquus Schumacher ( = avicularis 

 Lamarck), and this is quite possible. 



Anatomy. — A young specimen with soft parts is at hand, iirobably a male, 

 since no marsupial structure can be seen. 



Soft parts like those of Hijria. The palpi are slightly broader, and their 

 lower margins more curved. The anterior end of the inner gill is immediately 

 behind the palpi. Shape and structure of the gills normal. 



Subfamily Mutelin^ (See above, p. 457). 



"General Remarks. 



Shells of various shapes, subelliptical, subovate, subtrapezoidal, or more or 

 less rounded. Beak-sculpture absent, only in one case have sul)concentric bars 

 been observed, which, however, ma.\- not be homologous to the real beak-sculpture 

 of other Naiades. 



