506 MEMOIRS OF THE CARNEGIE MUSEUM. 



being immediately helaind the palpi. Inner lamina of inner gills entirely con- 

 nected with abdominal sac. Structure of the gills in the male as usual, but the 

 interlaminar tissue is unusually well-developed, forming a rather thick layer 

 chiefly on the inside of the primary limb of the gill; and it has, as usual, short, 

 interrupted interlaminar connections, elongated in the direction of the gill-filaments, 

 which in the middle of the gill are few and far apart, while they arc a little more 

 frequent near the ends. 



Lea describes the marsupium (of acutirostris) as occupying nearly the whole 

 length of the inner gill, but no information is given as regards the finer structure. 



Color of foot brown or blackish in the distal part, otherwise the soft parts are 

 whitish. 



14. DiPLODON CHARRUANUS (D'Oi'bigny) (1835). 



Glochidium: Text-fig. 4^, p. 4G9. 



Unio charruana D'Orbigny, 1843, p. 606, PI. 71, figs. 8-11; Pilsbry & Rush, 1896, 



p. 81; CoRsi, 1900, p. 447, fig. 31. 

 Unio faba (as form of charruana) D'Orbigny, 1843, p. 606 (text), as rhuacoica, 



PL 71, figs. 12-14 {in tabula per errorem, see Explanation of plates, p. 704). 

 Unio rhuacoica D'Orbigny, 1843, p. 606, PI. 69, figs. 4, 5; Corsi, 1901, p. 450, 



fig. 33. 

 U7iio ccthiops Lea, Obs., X, 1863, PL 41, fig. 285 (juv.). 

 Unio parens Lea, Obs., XII, 1869, PL 33, fig. 77 {juv.). 

 Diplodon rhuacoicus, charruanus, cetkiops, parens,. Simpson, 1914, pp. 1242, 1243, 



1247, 1256. 

 Diplodon hidalgoi Haas, 1916, pp. 18, 49, PL 1, fig. 1. 

 Diplodon parous Haas, 1916, pp. 16, 49. 

 Diplodon fortis Marshall, 1917, p. 382, PL 52, figs. 1-4. 



Type-locality. — Small streams from Maldonado and Montevideo to Las Vacas, 

 Uruguay ("Banda Oriental"). 



Other Localities. — Lake Potrero, Maldonado, Uruguay (Pilsbry & Rush); 

 Rio Canelon Grande, Montevideo (D'Orbigny, rhuacoica); Dep. Canelones, LTru- 

 guay (Corsi); Rio Miguelete, Uruguay (Haas, hidalgoi); Rio Negro, Tacuarembo, 

 LTruguay; correctly S. Fructuosa, on Rio Tacuarembo, tributary to Rio Negro 

 (Marshall, /o)7/'.s); Uruguay River (Lea, cetkiops). 



New Locality. — Pond along Rio Negro, Santa Isabel, Uruguay (J. D. Haseman 

 coll., February 11. 1909). About twenty-five specimens, seventeen with soft 

 parts, including males and gravid females. 



