NO. 1205. SYNOPSIS OF THE y.UAUESslMI'XO*. 591 



tMEDIONIDUS WALKERI B. H. Wright. 



* Unio walkeri B. H. WRIGHT, Naut., XI, 1897, p. 91. 



"Lampsilis walkeri SIMPSON, Pr. Ac. N. Sci. Phila.. 1900, p. 77, pi. i. rig. 5. 



Suwanee River, Florida; Ocklockonee River, Georgia. 

 (Group of Medionidits axbientus.) 



Shell elongate-elliptical, scarcely inflated, with an ill-defined poste- 

 rior ridge, the posterior slope being strongly, corrugately wrinkled; 

 beaks apparently sculptured with coarse, irregular, broken ridges, 

 somewhat doubly looped: epidermis bright, with broken rays which 

 sometimes form irregular patches, but are usually developed into 

 square spots; pseudocardinals rather small, stumpy; laterals rather 

 strong, club-shaped, generally showing traces of vertical striatiou; 

 nacre dull, bluish white. The female shell is very slightly inflated just 

 behind the center of the base, the male often becomes arcuate when old. 



Animal unknown. 



t MEDIONIDUS SUBTENTUS Say. 



*Unio snbtenttis SAY, Jl. Ac. N. Sci. Phila., V, 1825, p. 130; Am. Conch., I, No. 

 2, 1831, pi. xv.* CONRAD, Am. Jl. Sci., XXVI, 1834, p. 343, pi. i, fig. 1 ; * New 

 F.W, Shells, 1834, p.7L * FBKUSSAC, Guer. Mag., 1835, p. 26. * HOLLER, Syn. 

 Nov. Gen., 1836, p. 209. * CONRAD, Monog., X, 1838, p. 85, pi. XLVIII, fig. 1. 

 *HANLEY, Test. Moll., 1842, p. 176; * Biv. Shells, 1843, p. 176, pi. xx, tig. 34. 

 "CHENC, Bib. Conch., 1st ser., Ill, 1845, p. 25, pi. iv, figs. 2,2a, 2b. r CATLOW 

 and REEVE, Conch. Nom., 1845, p. 64. * CONRAD, Pr. Ac. N. Sci. Phila., VI, 

 1853, p. 258.* KUSTER, Conch Cab. Unio, 1856, p. 164, pi. XLVII, fig. 4. 

 r ll. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 497.* SOWKRBY, Conch. Icon., 

 XVI, 1868, pi. LXXII, fig. 370. *B. H. WRIGHT, Check List, 1888.* P.ETEL, 

 Conch. Sam., Ill, 1890. p. 168. 



* Margarita ( Unio) sttbtentus LEA, Syn., 1836, p. 13; 1838, p. 14. 

 *Maryaron ( Unio) subtentus LEA, Syn., 1852, p. 21; 1870, p. 32. 



*Unio sHbtenta DESHAYES, An. sans Vert., 2d ed., VI, 1835, p. 555; 3d ed., II, 1839, 

 p. 675. 



Tennessee and Cumberland River systems. 



Genus NEPHRONAIAS Crosse and Fischer, 1893. 



(Type, Unio plicatulus Charpeutier.) 

 Nepronaias CROSSE and FISCHER, Miss. Sci., Pt. 7, II, 1893, p. 556. 



Shell elliptical, biangulate behind, that of the male showing a tend- 

 ency to become arcuate with age, the female usually having a post- 

 basal inflation and never arcuate; surface concentrically sculptured; 

 beaks low, with faint broken ridges which show a tendency to fall into 

 two rounded loops; pseudocardinals generally rather compressed, rag- 

 ged, laterals obliquely ridged; cavity of the beaks rather deep, dorsal 

 muscle scars distinct, running in a line from the beak cavity downward 

 and forward. Animal with the branchiu- rounded below, outer the 

 larger behind, inner the larger anteriorly, free from the abdominal sac 



