PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



fDIPLODON TRIFIDUS Lea. 



* Unio trifidus, Lea, Pr. Ac. N. Sci. Phila., IV, 1860, p. 89; * Jl. Ac. N. Sci. Phila., 



V, 1863, p. 386, pi. XLiv, fig. 295 ; * Obs., X, 1863, p. 22, pi. xli v, fig, 295. 

 "^ Mar gar on {Unio) trifidus, Lea, Syn., 1870, p. 50. 



Argeutiiia. 



{(jvoVi^ oi Di'plodon pazi.) 



Shell subtrapezoidal, rounded in front and strongly biaugulate behind, 

 the wavy beak sculpture extending well over the disk ; epidermis olive; 

 pseudocardinals ragged, with a tendency to break into denticles. 



DIPLODON PAZI Hidalgo. 



* Castalia pazi Hidalgo, Jl. de Conch., XVI, 1868, p. 353, pi. xiii, fig. 6. — * P.etel, 



Conch. Sam., Ill, 1890, p. 189. 



Imbabura, Ecuador. 



DIPLODON HYL^AUS d'Orbigny. 



* Unio hylim d'Orbigny, Guer. Mag., 1835, p. 36; * Voy. Am. Mer., 1843, p. 607, pi. 



LXix, figs. 8, 9. 



* Margaron ( Unio) h.ijlaus Lea, Syn., 1852, p. 21; 1870, p. 31. 



* Unio hylwus H. and A. Adams, Gen. Rec. Moll., II, 1857, p. 497. — *Sowekry, 



Conch. Icon., XVI, 1868, pi. xciii, fig. 506.— ^P.etel, Conch. Sam., Ill, 1890, 

 p. 155. 



* Unio guaraniana d'Orbigny, Guer. Mag., 1835, p. 37; * Voy. Am. Mer., 1843, p. 



608, pi. Exix, figs, 10-12. 



Bolivia; Paraguay Kiver. 



(Group of Diplodon parallelipipedon.) 



Shell elongated, subtrapezoidal, inflated, obliquely truncated behind; 

 posterior ridge strong; beaks rather low, sculpture of nearly or quite 

 strictly radial bars with concave spaces between ; epidermis dark; pseu- 

 docardinals compressed in the young, granular, vertically striate and 

 breaking into denticles in the old shell; laterals long,curved, granular, 

 often vertically striate; anterior scars smooth, distinct. 



t DIPLODON PARALLELIPIPEDON Lea. 



* Unio parallelipi^)edon Lea, Tr. Am. Phil. Soc, V, 1834, p. 60, pi. Viii, fig. 20; 



*Obs., I, 1834, p. 172, pT. viii, fig. 20.— * d'Orbigny, Guer. Mag., 1835, p. 34.— 

 *Hanley, Test. Moll., 1842, p. 205; Biv. Shells, 1843, p. 205.— * d'Orbigny, 

 Voy. Am. Mer., 1843, p. 609.—^ Catlow and PtEEVE, Conch. Nom., 1845, p. 62.— 

 *II. and A. Adams, Gen. Kec. Moll., II, 1857, p. 491.— "Kuster, Conch. Cab. 

 Unio, 1861, p. 220, pi. Lxxiv, fig. 2.—* Sowerby, Conch. Icon., XVI, 1868, pi. 

 Lxxxix, fig. 478.— "^ PiETEL, Conch. Sam., Ill, 1890, p. 162. 



* Margarita ( Unio) parallelipipedon Lea, Syn., 1836, p. 35 ; 1838, p. 24. 



* Margaron ( Unio) parallelipipedon Lea, Syn., 1852, p. 36; 1870, ji. 58. 



f Unio honplandi Valenciennes, in continuation of Humboldt's Zool. Obs., 1827.' 



Rio de la Plata system. 



' According to Lea. I have not seen this paper, and Lea does not cite the page, 

 A specimen with the above label from the Morelet collection = parallelipipedon Lea. 



