582 MEMOIRS OF THE CARNEGIE MUSEUM. 



ing from the swellings, toward the inner lamina (secondary limb) stretch out, and 

 that the egg-masses are located only in this part of the water-tubes, while the 

 part toward the outer lamina (primary limb) does not contain eggs, and forms 

 what should be called secondary water-tubes. In the sterile female the swelling 

 of the septa (vertical ridges i)rojecting into the water tubes) arc located as usual. 

 In the cross-section of the gills of the male (PI. XLVIII, fig. 7a) it is seen, chiefl.y 

 in the inner gill, that the alternation of stronger and weaker septa is due to the 

 alt(>rnating presence or absence of a larger blood-vessel at the point where the 

 septum connects with the primary limb. In the marsupial gill of the female this 

 is obscured in the direct view by the development of the ridges, so that the sei)ta 

 appear more uniform. 



The contents of the charged marsupium consist of small globular embryos in 

 an early stage of development. No lasidia were seen. Von Ihering (1891, p. 

 480) mentions the eggs of Aplodon pazi. They are small, 0.075 mm. in diametcM-. 



45a. MoNOcoNDYL^A MiNUANA PARCH APPi (D'Orbiguy) (1835). 

 Mnnocondyla'a parchappi D'Orbigny, 1843, p. 615, PI. 68, figs. 1-3; Simpson, 



1900, p. 911; 1914, p. 1386; Haas, 1916, pp. 24, 54. 



Type-locality. — Rio Parana, Itaty, Province Corrientes, Argentina. 



Other Locality. — Rio Uruguay, 8alto Oriental, Uruguay (Haas). 



New Locality. — Rio Jacuhy, C'achoeira, Rio Grande do Sul, Brazil (J. D. Hase- 

 man coll., January 26, 1909). One specimen, male with soft parts. 



Distribution. — Rio Parana and Rio Uruguay, and also Guahyba-drainage. 

 The distribution resembles that of M. minuana. 



D'Orbigny has already pointed out the close resemblance of this form to M. 

 minuana, but gives as differentiating characters the greater compression of the 

 shell, the less elevated and less incurved beaks, the absence of a lunula, and the 

 rose-colored nacre. We may dismiss the last two characters as unimportant, 

 since the lunula is variable and generally less developed in forms with lower beaks; 

 and since reddish nacre is found as an individual variation in other species of 

 Monocondylcea. But the greater compression of the shell and the feebler develop- 

 ment of the beaks is striking. In D'Orbigny's figure, as well as in my specimen, 

 the latter character is connected with a straighter hinge-line, which is much less 

 incurved below the beaks. 



We have seen that specimens of minuana sometimes approach parchappi in 

 the less pronounced obesity. The same may be said of the inflation of the beaks 

 and the curvature of th(> hinge-line. However, none of my s]iecimens recorded as 



