DIPI.ODON 1285 



pseudocardinals irregular and much split up ; laterals curved, 

 strong, two in the left valve and one in the right ; muscle 

 scars small ; nacre whitish, sometimes dull purple in' the cavi- 

 ties, much thicker in front. 



Length 92, height 78, diam. t,?< mm. 



Length TOO, height 76, diam. 47 mm. 



L^ruguay and Parana rivers. 

 Unio paraneiisis Lka, Tr. Am. Phil. Soc, V, 1834, pi. xiv, 



fig. 42; Obs., I, 1834, p. 211, pi. XIV, fig. 42. — Hanley, Biv. 



Shells, 1843, P- 202, pi. XXI, fig. 3. — KusTER, Conch. Cab. 



L^nio, 1861, p. 253, pi. Lxxxv, fig. 3. — Sowerby, Conch. Icon., 



XVI, 1866, pi. I.I, fig. 268. 

 Margarita (Unio) parancnsis Lha. Syn., 1836, p. 33 ; 1838, p. 



23- 



Margaron (^Unio) parancnsis Lea, Syn., 1852, p. 34; 1870. p. 



55- 

 Diplodon parancnsis Simpsox. Syn., tqoo, p. 887. 



Apparently abundant and C|uite variable in form and color 



of epidermis. 



DiPL(.>DON NocTT.TRNus (LcaV 



Shell short obovate, convex, rather solid, inequilateral, nar- 

 rowed and rounded in front, full in the post-dorsal and post- 

 basal regions; beaks somewhat elevated but not inflated; sur- 

 face unevenly sulcate ; epidermis dark, scarcely shining, green- 

 ish-brown, the hinder half of the shell being much darker; 

 pseudocardinals small, two in each valve ; there are two small 

 laterals in the left valve and one in the right ; muscle scars 

 small ; nacre lurid whitish, thicker in front. 



Length y2. height 60, diam. 28 mm. 



Uruguay River. 

 Unio nochirnus Lea, Pr. Ac. X. Sci. Phila., IW i860, p. 91 ; 



Jl. Ac. X. Sci. Phila., V, 1863, p. 380, pi. xiji. fig. 288; Obs., 



X, 1863, P- 16, pi. XLTI, fig. 288. 

 Margaron (Unio) nocturniis Lea, Syn., 1870, p. 56. 

 Diplodon parancnsis (part), Simpson, Syn., 1900, p. 887. 



At the time I wrote the Synopsis the type of this latter shell 

 was mislaid. Lea states in his description that it is without 



