752 PROCEEDINGS OF THE NATIONAL MUSEUM. VML.XXII. 



* CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 245. *H. and A. ADAMS, Gen. 

 Rec. Moll., II, 1857, p. 495.* CHENU, 111. Conch., 1858, pi. xxn. figs. 5, 5o, 56. 

 *KUSTEK, Concb. Cab. Unio, 1862, p. 279, pi. xciv, fig. 3. *SOWERBY, Conch. 

 Icon., XVI, 1866, pi. XLI, fig. 227.* B. H. WRIGHT, Check List, 1888.* P/ETKL, 

 Conch. Sam., Ill, 1890, p. 146. 



*Margaron (Unio) biybyensis LEA, Syn., 1852, p. 24, 1870, p. 38. 



Tennessee River drainage; Indian Territory? Texas? The two last 

 localities very doubtful. 



(Group of Pleurobema decisa.) 



Shell solid, inflated, ovate to elliptical, very inequilateral, somewhat 

 truncated in front and rounded or bluntly pointed behind, wedge- 

 shaped when looked at from above; base slightly angled in front, then 

 nearly straight for two-thirds of its length, from whence it curves to 

 the posterior point; beaks high, curved inward and forward; beak 

 sculpture consisting of a few coarse, irregularly concentric ridges 

 which curve slightly upward behind; epidermis tawny to brownish, 

 rayless, the rest periods very distinctly marked by dark bands; pseudo- 

 cardinals stumpy, ragged, often showing a" tendency to elongation in 

 the direction of the axis of the shell. 



Animal having the branchiae rather small, inner the larger, free nearly 

 or quite the entire length of the abdominal sac, marsupiuni occupying 

 all but the extreme posterior end of the outer gills; branchiae and anal 

 openings papillose. 



t PLEUROBEMA DECISA Lea. 



* Uwiodecisj/sLEA, Tr. Am. Phil. Soc., IV, 1831, p. 92, pi. xn, fig. 23; * Obs., 1, 1834, 



p. 102, pi. xn, fig. 23.* CONRAD, New F. W. Shells, 1834, p. 68.* FERUS- 

 SAC, Guer. Mag., 1835, p. 28. * CONRAD, Monog., I, 1835, p. 6, pi. in, fig. 2. 

 *HANLEY, Test. Moll., 1842, p. 187; Biv. Shells, 1843, p. 187, pi. xxn, fig. 21. 



* CATLOW and REEVE, Conch. Nom., 1845, p. 58.* KUSTER, Conch. Cab. Unio, 

 1852, p. 41, pi. vn, fig. 3. 1 * CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 248. 

 *H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 495.* CHENU, 111. Conch., 

 1858, pi. xvin, figs. 3, 3a, 36.* REEVE, Conch. Icon., XVI, 1864, pi. xvi, fig. 

 71. B. H.WRIGHT, Check List, 1888.* P^ETEL, Conch. Sam., Ill, 1890, p. 150. 



* Margarita (Unio) decisus LEA, Syn., 1836, p. 21; 1838, p. 18. 

 *Margaron (Unio) decisux LEA, Syn., 1852, p. 26; 1870, p. 40. 



* Unio scalenius SAY, Am. Conch., VI, 1834. 



t* Unio anaticulus LEA, Pr. Ac. N. Sci. Phila., V, 1861, p. 40; "Jl. Ac. N. Sci. Phila., 

 1862, p. 92, pi. xni, fig. 240; *Obs., VIII, 1862, p. 96, pi. xm, fig. 240. 

 *SOWERBY, Conch. Icon., XVI, 1866, pi. xxxvn, fig. 199. *B. H. WRIGHT, 

 Check List, 1888. * P.ETEI., Conch. Sam., Ill, 1890, p. 144. 



*Margaron ( Unio) anaticulus LEA, Syn., 1870, p. 40. 



*Unio consanguineus LEA, Pr. Ac. N. Sci. Phila., VI, 1861, p. 60; *J1. Ac. N. Sci. 

 Phila., V, 1862, p. 67, pi. vn, fig. 217 ; * Obs., VIII, 1862, p. 71, pi. vn, fig. 217. 

 *SOWERBY, Conch. Icon., XVI, 1868, pi. LXXVIII, fig. 409. *B. H.WRIGHT, 

 Check List, 1888. *PJCTEL, Conch. Sam., Ill, 1890, p. 148. 



*Margaron ( Unio) consanguineiis LEA, Syn., 1870, p. 40. 



1 This figure is probably that of U. decisus. That on plate vm, which he refers to 

 that species, is most likely Lea's raveneliamis. 



