480 MEMOIRS OF THE CARNEGIE MUSEUM. 



Anatomy. — I have before me many males and gravid females with soft parts. 

 It should be noted that the smallest gravid females are only 16 mm. long and that 

 this fact indicates that this is a small species, not growing to a larger size, as my 

 material shows, reaching the maximum length of 28 mm. 



Anal opening short, slightly shorter than the branchial opening, the latter 

 very short, with few but distinct papilliB. Palpi subtriangular, lower margins 

 convex, posterior margins scarcely connected. Gills normal. Inner lamina of inner 

 gill entirelj^ connected with abdominal sac. In the larger gravid females the 

 middle of the inner gill is marsupial, leaving a little less than one-fourth of the 

 gill both at the anterior and posterior ends non-marsupial. In the smaller females 

 the marsui>ial part is smaller. The swelling of the charged marsupium is moderate 

 and the gills are charged to near the edge. In the marsupial part the interlaminar 

 connections are arranged in interrupted vertical septa. Since no sterile females 

 are at hand, the exact arrangement could not be seen in a face view, but from sec- 

 tions (Plate XLVII, fig. 5) it is evident that it is very likely more or less reticulate. 



Glochidia (Text-fig. 4a, p. 469) subtriangular and margined, without hooks. 

 Measurements, without margin: L. 0.30 to 0.31 mm.; H. 0.24 to 0.25 mm.; with 

 margin: L. 0.35 to 0.36 mm., H. 0.29 to 0.30 mm. The presence of eggs and 

 glochidia on July 20 should be recorded with respect to the breeding season. 



Color of Soft Parts in Alcohol. — Foot blackish in its distal part, this color 

 separated in a sharp line from the light basal part. Rest of soft parts whitish. 



4. DiPLODON TRiFiDUS (Lea) (1860). 

 Diagram of Soft Parts (See Text-fig. 1, p. 455). 

 Unio trijidus Lea, Obs. X, 1863, PI. 44, fig. 295. 

 Diplodon trifidus Simpson, 1900, p. 884; 1914, p. 1272. 



Type-locality. — "Buenos Ayres." Never reported again since its original 

 description. 



New Localities. — Centre of Rio Guapore, near Rio Sao Simao, Matto Grosso, 

 Brazil (J. D. Haseman coll., July 20. 1909). Six specimens, all with soft parts. 

 In the three smallest the sex is uncertain (they have the male structure) ; the others 

 are two males and one (the largest) a gravid female with eggs. Rio Guapore, Sao 

 Antonio de Guapore, Matto Grosso, Brazil (J. D. Haseman coll., July 31, 1909). 

 One male with soft parts. 



Distribution. — I have doubts as to the correctness of the locality originally 

 given. Von Ihering (1893, p. 118) lists this species with those from the La Plata 

 drainage, but he rests entirely upon Lea. The latter received his single specimen 



