ortmann: south American naiades. 541 



Gills long and wide, i)osteriorly of about the same width, but anteriorly the 

 inner is wider. Outer gill with margin curved, much narrower anteriorly, its 

 anterior end near the highest point of the mantle-attachment-line. Margin of 

 inner gill nearly straight in the middle, anteriorly this gill is a little narrowed, 

 its anterior end immediately behind the palpi. Inner lamina of inner gill entirely 

 connected with abdominal sac. 



Non-marsupial gills with scattered, short, interrupted intcrlaminar connec- 

 tions, elongated in the direction of the gill-filaments. The marsupium of the 

 female (pi. XLVII, fig. 1) is in the inner gill, leaving free a small anterior and 

 posterior section, about one-fourth in front, and a little more behind, so that the 

 marsupium is located in the middle of the gill, but slightly more anteriorly. The 

 intcrlaminar connections (See also pi. XLVIII, fig. 4) are developed as rather 

 regularly interrupted septa, forming intercommunicating, incomplete water-tubes. 

 In the middle and at the base of the marsupium, the connections fall also into 

 irregular transverse lines, with a suggestion of quincuncial arrangement. In 

 young females, the marsupial part of the inner gill is considerably smaller. 



It should be noted that the non-marsupial gills in this species are more nearly 

 normal than in D. gratus. 



27. DiPLODON ROTUNDUS Spix (1827). 



Diplodon rotundum and Unio rotundus Spix & Wagner, 1827, p. 34, PI. 25, figs. 3,*4. 

 Unio rotundus Sowerby, XVI, 1868, PI. 72, fig. 369; Von Ihering, 1890, p. 169, PI. 



9, fig. 10; 1910, p. 139. 

 Diplodon {Cydomya) rotundus Simpson, 1900, p. 886; 1914, p. 1282. 



Type-locality.— Honthern Brazil. 



Other Localities. — Rivers of eastern Brazil (Von Ihering, 1890) ; Rio S. Fran- 

 cisco, Villa Nova, Sergipe, Brazil (Von Ihering, 1910); Rio Paraguassii, Bahia, 

 Brazil (Von Ihering, 1893, p. 115; 1910); Rio Parahyba do Sul, Rio de Janeiro, 

 Brazil (Von Ihering, 1893, p. 115). 



New Locality. — Rio S. Francisco, Bom Jesus da Lapa, Bahia, Brazil (J. D. 

 Haseman coll., December 17, 1907). Two odd right valves. 



In the Carnegie Museum there is another, complete specimen from the Hart- 

 man collection without locality. 



Distribution. — Known from the lower and middle part of the Rio S. Francisco, 

 Rio Paraguassii, and Rio Parahyba do Sul in eastern Brazil. 



According to the descriptions given by Von Ihering and Simpson my specimens 

 belong here, but my material is too scanty to give a full account of the species. 



