ortmann: south American naiades. 



593 



Anodontites tenebricosiis Simpson, 1914, p. 1448. 

 Anodontites {Styganodon) tenebricosus Haas, 1916, pp. 35, 57. 



Type-locality. — Rio Parana. 



Other Localities. — Rio San Jose and Arroyo del Rosario, Uruguay (D'Orbigny) 

 (tributaries to La Plata in the Banda Oriental); Rio de la Plata, Buenos Aires, 

 Argentina (D'Orbigny); Buenos Aires (Haas); Rio Uruguay, Salto Oriental, Uru- 

 guaj' (Haas) ; Rio Piracicaba, Piracicaba, Sao Paulo, Brazil (Von Ihering) (Nehring). 



New Localities. — Pond along banks of Rio Negro, Santa Isabel, Uruguay (J. 

 D. Haseman coll., February 11, 1909). One complete specimen and one left valve. 

 Rio de la Plata, San Isidro, 20 km. North of Buenos Aires, Argentina (A. Wind- 

 hausen coll., January, 1917). One female with soft parts. 



Distribution. — From the region of Buenos Aires in the La Plata system and 

 its tributaries in Uruguay (smaller streams of the Banda Oriental and Rio Uruguay- 

 system) up the Parana River to its headwaters in Sao Paulo, Brazil. 



Simpson gives a much larger range, adding even Ecuador and Peru, but I do 

 not know on what authority. 



This species is well known and has been well described. Its chief characters 

 are its shape, which, although elongated-subtrapezoidal, is rather short and high 

 in comparison with the related species. The prismatic border of the shell, chiefly 

 in old shells, is remarkably wide, but subequal in width, not suddenly changing 

 anywhere. 



The character of the epidermis has been given as concentrically lamellose. 

 This is correct, and the fine, crowded, concentric lameUse are very obvious. How- 

 ever, closer investigation shows that between these lamellae are additional, more 

 irregular wrinkles, which produce upon the posterior part of the shell a reticulated 

 (anastomosing) sculpture, and more anteriorly these wrinkles may be even radial. 

 But they exist only between the concentric lamella;, and thus they are very short 

 and largely obscured by the concentric sculpture. This difference of sculpture 

 from that of A. crispata is very striking. Otherwise these two species have many 

 features in common. 



Measurements. 



Sex. 



Length. 



Height. 



Beaks. 



S. Isabel . 

 S. Isidro . 



57 mm. 1 33 mm. =5S jjr. ct. of L. 

 92 " I 54 '• =59 



17 mm. =29pr. ct. of L. 

 32 " =35 



at 18 mm. =32 pr. rt. of L. 

 27 '• =29 



According to Von Ihering's measurements, the height is 53 pr. ct. and the 

 diameter 34 pr. ct. of length. According to Nchring's measurements the height is 

 48 to 55 pr. ct., the diameter 30 to 33 i)r. ct. Thus specimens from the upper 



