ortmann: south American naiades. 



519 



The following references should be added to those given by Simpson. 

 Unio delodonta D'Orbigny, 1843, p. 605; Corsi, 1901, p. 449. 

 Diplodon wymani Haas, 1916, pp. 12, 47. 



As to the synonymy compare Simpson. His D. wymani only in part belongs 

 here. D. apprimus Lea, miited by him with wymani, is different (more swollen, 

 see above p. 512). On the other hand, I cannot distinguish the real wymani from 

 ladeolus, and Von Ihering (1893, p. 117) also unites them. 



Type-locality. — Rio de la Plata. 



Other Localities. — Stream, Villa del CVrro, Montevideo, Uruguay (D'Orbigny); 

 Rio Uruguay (Lea, in/mani) ; Rio Uruguay, Las dos Hermanas Islands, Uruguay 

 (D'Orbigny); Rio Uruguay, Salto Oriental, Uruguay (Haas); Rio San Salvador 

 (trib. to Uruguay), Soriano, Uruguay (Corsi); Buenos Aires (D'Orbigny); Rio 

 Batel and Rio C'orrientes, Province of Corrientes, Argentina (D'Orbigny). 



New Localities. — Pond near Rio Negro, Santa Isabel, Uruguay (J. D. Haseman 

 coll., February 11, 1909). One specimen, young. Brooklet, two miles north 

 of the City of La Plata, Argentina (Dr. W. J. Holland coll., September 24, 1912). 

 Two specimens. 



Distribution. — Lower La Plata and Parana systems, upward to the province of 

 Corrientes; also in the lower Uruguay and Rio Negro, and small tributaries of the 

 La Plata in Argentina and Uruguay. 



INIy specimens from La Plata are typical. The young specimen from Santa 

 Isabel is interesting in having a ra-ther high shell, which is slightly oblique, but 

 comparison with the other specimens shows that, according to the growth-rests, 

 the latter had the same shape when young. This j'oung shell also exhibits the 

 comparatively heavy beak-sculpture, with the radial bars running down the shell 

 about 13 to 15 mm. Traces of these are also seen in my larger specimens. 



The first measurements given by Simpson ap])ar(>ntly r(>fer to the type of 

 lacteolus, although they do not fully agree with Lea's figure. The second measure- 



