604 PROCEEDINGS OF THE NATIONAL MUSEUM. 



Vert., 2d ed., VI, 1835, p. 550; 3d ed., II, 1839, p. 673.* HANLEY, Test. Moll., 

 1842, p. 184 ; * Biv. Shells, 1843, p. 184, pi. xx, fig. 51.* CATLOW and REEVE, 

 Conch. Norn., 1845, p. 64. *CHENU, 111. Conch., 1858, pi. xvi, figs. 4, 4a, 46. 

 *H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 496. *CHENU, Man., II, 

 1859, p. 138, fig. 671. *SOWERBY, Conch. Icon., XVI, 1868, pi. LXi, fig. 304. 



* B. H. WUIGHT, Check List, 1888. 



* Margarita ( Unio) securis LEA, Syn., 1836, p. 19; 1838, p. 16. 

 *Margaron ( Unio) securis LEA, Syn., 1852, p. 24 ; 1870, p. 37. 

 *Playiola securis SMITH, Bull. U. S. Fish Cora., 1899, p. 291, pi. LXXX. 



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



*Flagiola lineolata AGASSIZ, Arch, fur Nat., 1, 1852, p. 48. 



*Unio lineolatus CONRAD, New F. W. Shells, 1834, p. 70. *FERUSSAC, Guer. Mag. 

 1835, p. 28. * CONRAD, Am. Conch, (continuation), VII, pi. LXVIII (no date). 



* CONRAD, Pr.Ac. N. Sci. Phila., VI, 1853, p. 251. * KUSTER, Conch. Cab. 

 Unio, 1861, p. 171, pi. Lin, figs. 1, 2. 



Mississippi drainage south into Arkansas; west into eastern Iowa 

 and Kansas; Tombigbee and Alabama river systems. 



Submenus AMYGDALONAIAS Crosse and Fischer. 1893. 

 (Type, Unio cognatus Lea.) 



Shell inflated, decidedly truncated at the posterior slope, surface 

 slightly concentrically sculptured; posterior ridge sharp and well 

 denned; epidermis shining, sometimes wrinkled looped, and painted 

 with a beautiful pattern of broken or arrow-marked rays; area of the 

 beaks flattened off in the direction of the axis of the shell, but not 

 compressed; beak sculpture delicate, somewhat broken and doubly 

 looped, the anterior loop rounded, the posterior sharp below, the ribs 

 fading out where they cross the posterior ridge; hinge delicate, pseudo- 

 cardinals rather compressed, high, and ragged; hinge plate narrow; 

 female shell very slightly swollen at post base. 



Animal with branchi.ne more or less free from the abdominal sac; mar- 

 supiuin consisting of numerous distinct ovisacs, and having a well- 

 marked sulcus extending around it at some distance above its base; 

 mantle thickened and doubled on its edge, which has dark papilla). 



(Group of Plagiola elegans.) 



Shell short, triangular oval, inflated, with a very sharp posterior ridge, 

 extending from the beaks to the hinder point of the shell; male and 

 female shells scarcely distinguishable, both being much expanded in 

 the basal region. 



t PLAGIOLA ELEGANS Lea. 



* Unio elegans LEA, Tr. Am. Phil. Soc., IV, 1831, p. 83, pi. ix,fig. 13; * Obs., 1, 1834, 



p. 93, pi. ix, fig. 13.* HANLEY, Test. Moll., 1842, p. 183 ; * Biv. Shells, 1843, p. 

 183, pi. xxi, fig. 33.* CATLOW and REEVE, Conch. Nom., 1845, p. 58.* H. and 

 A. ADAMS, Gen. Rec. Moll., II, 1857, p. 495. * CHENU, 111. Conch., 1858, pi. xv, 

 figs. 3, 3o, 3fc; * Manual, II, 1859, p. 138, fig. 672. *SOWERBY, Conch. Icon., 

 XVI, 1868, pi. LXXIV, p. 380.* CALKINS, Pr. Ottawa Ac. N. Sci., 1874, p. 42. 



* B. H. WRIGHT, Check List, 1888. 



* Margarita ( Unio) elegans LEA, Syn., 1836, p. 18; 1838, p. 16. 

 *Margaron ( Unio) elegans LEA, Syn., 1852, p. 23; 1870, p. 36. 



