ortmann: south American naiades. 531 



Color. — Distal part of foot dark l)rowiiish, jirayish, or blackish; the rest of 

 the soft parts arc whitish. 



Anal opening closed above; the closed part about four times as long, or a little 

 longer than the open ])art; the latter slit-like, slightly shorter than the branchial 

 opening. The latter with small, but distinct papilhe, separated from the anal by 

 a solid mantle-union. Palpi subtriangular, moderately large, of the usual shape; 

 their posterior margins connected at base. 



Gills rather long and wide. Outer gill subtriangular, widest at the beginning 

 of the posterior third, and here it projects a little beyond the inner gill. Inner gill 

 subtrapezoidal, its anterior end immediately liehind the jiali^i. Inner lamina of 

 inner gill connected with abdominal sac. 



Structure of non-marsupial gills as usual. In the female, the marsupiuni (PL 

 XLVI, fig. 6) is located in the inner gill, and in large specimens it is restricted to 

 the middle part of the gill, leaving non-marsupial almost one-third at the anterior 

 end, and a somewhat smaller portion at the posterior end. In young specimens 

 the marsupium is smaller. When charged, the marsupium forms a slighth' swollen, 

 lenticular, roimded, or oblong patch in the middle of the gill, most of it lying behind 

 the middle. The interlaminar connections of the marsupium are strongl.y de- 

 veloped, forming very incomplete, interrupted septa, and arranging themselves 

 rather in transverse and oblicjue rows, so that the vertical septiform structure is 

 obscure, while a reticulate and irregularly quincuncial arrangement prevails. 

 Only near the margin of the gill is a septiform structure indistinctl.y indicated. 

 The egg-masses do not conglutinate into placentae-like structures. 



Only one of my females has very young glochidia. They are, as far as can be 

 seen, of the usual shape, subtriangular, and somewhat oblique. Exact measure- 

 ments could not be obtained. No hooks are visible, but, of course, such may be 

 present in ripe glochidia. 



24. DiPLODON ENNO Ortmann, sji. nov. 

 Shells: Plate XXXVIII, figs. 5, 6, 7, 8; Anatomy of gills: Plate XLVI, fig. 7. 



Type-locality. — Rio Grande, Boqueirao, Bahia, Brazil (S. Francisco drainage). 

 (J. D. Haseman coll., January 9, 1908). Type-set: Cam. Mus. Cat. No. 31.9264. 

 Eighteen specimens, males and barren females, with soft parts. (A number 

 of additional .young specimens were in the original set.) 



According to the latest census of the Naiades from the Rio S. Francisco 

 drainage (Von Ihering, 1910, p. 138), there are only two species of Diplodon present 

 in this system: D. rofinidus Sjiix, and D. elli])ticus Sjiix. The former is much 



