884 pitocEEniycs or Tin: \.IT/O\.IL v/ >/.r.i/. 



tDIPLODON TRIFIDUS Lea. 



I 'nio trifidus, LEA, Pr. Ac. N. Sci. Phila., IV, 1X60, p. 89; * Jl. Ac. N. Sci. Phila., 



V, 1863, p. 386, pi. XLIV, fig. 295; * Obs., X, 1863, p. 22, pi. xi.iv, fig. 295. 

 Mnnjnron ( I'nio) trifidus, LEA, Syn., 1870, p. 50. 



Argentina. 



(Group of Diplodon pazl.) 



Shell subtrapezoidal, rounded in front and strongly triangulate behind, 

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

 pseudocardiuals ragged, with a tendency to break into denticles. 



DIPLODON PAZI Hidalgo. 



* Castalia pazi HIDALGO, Jl. de Conch., XVI, 1868, p. 353, pi. xin, fig. 6. * P.KTEL, 



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



Imbabura, Ecuador. 



DIPLODON HYL^AUS d'Orbigny. 



* Unio hyla'a D'ORBIGNY, Guer. Mag., 1835, p. 36 ; * Voy. Am. Mcr., 1843, p. 607, pi. 



LXIX, figs. 8, 9. 

 *Margaron ( Unio) hylceus LEA, Syn., 1852, p. 21; 1870, p. 31. 



* Unio hylceus H. and A. ADAMS, Geu. Rec. Moll., II, 1857, p. 497. *SOWEKHY, 



Conch. Icon., XVI, 1868, pi. xcm, fig. 506. *P.KTEL, Conch. Sam., Ill, 1890, 

 p. 155. 



* Unio gnaraniana D'OKBIGNY, Guer. Mag., 1835, p. 37; * Voy. Am. Mer., 1843, p. 



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



Bolivia; Paraguay River. 



(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. 



tDIPLODON PARALLELIPIPEDON Lea. 



* Unio parallelipipedon LKA, Tr. Am. Phil. Soc., V, 1834, p. 60, pi. vin, fig. 20; 



*Obs., 1, 1834, p. 172, pi. vin, 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. G09. * CATLOW and REEVE, Conch. Norn., 1845, p. 62. 

 *H. and A. ADAMS, Gen. Rec. 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. * P.ETEL, Conch. Sam., Ill, 1890, p. 162. 



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

 * Margaron ( Unio) parallelipipedon LEA, Syn., 1852, p. S6; 1870, p. 58. 



f Unio Itonplandi VALENCIENNES, in continuation of Humboldt's Zool. Obs., 1827. 1 



Rio de la Plata system. 



1 According to Lea. I have not seen tins paper, and Lea does not cite the page. 

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



