516 MEMOIRS OF THE CARNEGIE MUSEUM. 



Verj^ few species of Diplodon are known in Rio Grande do Sul, from the drainage 

 of the Guahyba (to which the Rio Jacuhy belongs)and all have been only incident- 

 ally mentioned by Von Ihering (1893). Under U. a'thiops piracicabana (I. c, p. 

 102) he reports that U. cethiops is found in the Guahyba River. I have been unable 

 to discover this species, which is identical with charruanus, in the material col- 

 lected by Haseman in this system, and I am sure that the present form is iiot the 

 one which Von Ihering calls cethiops. From his casual remarks it is seen that the 

 latter has a shallow depression on the disk (/. c, p. 104), and nothing of the kind 

 is seen in D. hUdcc. 



Anatomy. — I have two barren females, and three gravid females with glochidia. 

 Of the latter, one had only very few glochidia in the marsupium, but some were 

 in the suprabranchial canals, and thus it was evidentl}' discharging. The rest 

 of my specimens are males. 



Color of soft parts whitish; distal part of foot grayish black. 



Anal opening closed above; closed part about four times as long as the open 

 part, the latter slit-like, slightly shorter than the branchial; the latter has small, 

 but distinct pajiilke. Anal and branchial openings separated by a solid mantle- 

 connection. Paljii moderate, sul)triangular, posterior margins connected at base. 



Gills long and rather wide. They are about equally wide posteriorly, but the 

 outer is subtriangular and narrows anteriorly, while the inner does not, and re- 

 mains as wide as posteriorly, with its anterior end immediately behind the palpi. 

 Inner lamina of inner gill entirely connected with abdominal sac. The non- 

 marsupial gills with scattered interlaminar connections. In the female, the mar- 

 supium (Plate XLVI, fig. 3) is located in the inner gill, but anteriorly about one- 

 third of the gill remains non-marsupial, posteriorly much less, about one-fifth of 

 it or less, so that the marsupial part is located distinctly more backward in the 

 gill, occupying about half of its length. When charged, the marsupium forms a 

 slightly swollen patch. In young specimens the marsupium is smaller. Inter- 

 laminar connections in the marsupium forming septiform rows, with a tendency 

 to fall also into irregular transverse rows. The transverse arrangement prevails 

 near the base and in the middle of the gill, here and there with a suggestion of a 

 quincuncial disposition; the septiform arrangement is found toward the margin 

 of the gill. 



Glochidium (Text-fig. 4i, p. 469) subtriangular, longer than high, with a ventral 

 point, slightly oblique, the point being vertically under the posterior end of the 

 upper margin. There are no hooks. In one of my specimens, the glochidia are 

 not margined (not mature); in the two others they are margined, with a narrow 



