510 MEMOIRS OF THE CARNEGIE MUSEUM. 



tions. The marsupial part of the female occupies a large portion of the inner gill, 

 leaving about one-fourth of the gill free in front, and a smaller part free behind, 

 thus gravitating slightly toward the posterior part of the gill. The interlaminar 

 connections could not be distinctly observed by me on a lateral view, since no Ijarren 

 females are at hand; but from sections it was possible to infer that they form in- 

 terrupted septa forming a system of intercommunicating water-tubes. The eggs 

 and glochidia fill the water-tubes and the perforations of the septa in a mass, which 

 is not conglutinated and divided into placentae. 



The (jlocliidium (Text-fig. Ag, p. 469) has the characteristic triangular shape, 

 somewhat oblique, with the point situated below the posterior end of the upper 

 margin (like the figure of the glochidium of U. peculiaris, See Lea, Obs. XII, 1869, 

 PI. 34, fig. 80). This point does not possess a hook. Size of glochidium: L. 0.31, 

 D. 0.26 mm. 



I have examined the glochidia of three specimens; one of these had the mar- 

 supium largely empt}^ and thus it appears to have been discharging. Yet no hooks 

 were seen. But it may be that the discharge in this case was premature, that 

 none of the glochidia were mature, and that the hooks might have developed later. 

 This can be decided only by investigating more material. 



15. DiPLODON PICEUS (Lea) (1860). 

 Anatomy of gills: PL XLVI, fig. 2; glochidium: Text-fig. 4/;, p. 469. 

 Unio piceus Lea, Obs., X, 1863, PI. 41, fig. 287. 

 Diplodon piceus Simpson, 1914, p. 1244; Haas, 1916, pp. 15, 49. 



Type-locality. — Uruguay River. * 



Other Localities. — Rio Uruguay, Salto Oriental, Uruguay (Haas); Rio Migue- 

 lete, Uruguay (Haas). 



Localities Represented in the Carnegie Museum. — Rio Uruguay (in mud), 

 Uruguayana, Rio Grande do Sul, Brazil (J. D. Haseman coll., February 5, 1909) 

 eight specimens, seven of them with soft parts, males and gravid females. Arroyo 

 Miguelete, Montevideo, Uruguay (J. D. Haseman coll., February 17,1909) one 

 specimen. 



Distribution. — Positively known from the Uruguay River, and from a small 

 coastal stream (R. INIiguelete) near Montevideo, and probably more widely dis- 

 tributed in the "Banda Oriental" in Uruguay. It possibly may be only a form of 

 charruanus. Corsi does not mention it from Uruguay. 



A species closely allied to D. charruanus, and very near to it in its dimensions, 

 except that it does not show the same extremes of variation. It is, however, 



