604 PBOCEEBINaS OF THE NATIONAL MUSEUM. vol.xxii. 



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

 1842, p. 184 ; * Biv. Shells, 1843, p. 184, pi. xx, fig. 51.—* Catlow and Eeeve, 

 Conch.Nom.,1845,p.64.—*CHENU, 111, Conch., 18.58, pi. xvi, figs. 4, 4a, 46.— 

 *H. and A. Adams, Gen. Rec. Moll., 11, 1857, p. 496.— *Chenu, Man., II, 

 1859, p. 138, fig. 671.— *SowERBY, Conch. Icon., XVI, 1868, pi. lxi, fig. 304.— 



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



*MargarUa ( Unio) securis Lea, Syn., 1836, p. 19; 1838, p. 16. 

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

 *Pla(jiola securis Smith, Bull. U. S. Fish Com., 1899, p. 291, pi. lxxx. 



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



*Plagiola lineolata Agassiz, Arch, flir 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. Liii, figs. 1, 2. 



Mississippi drainage south into Arkansas; west into eastern Iowa 

 and Kansas; Tombigbee and Alabama river systems. 



Subgenus AMYGDALONAIAS Crosse and Fischer. 1893. 

 (Type, Unio cognatus Lea.) 



Shell inflated, decidedly truncated at the i)osterior slope, surface 

 slightly concentrically sculptured; posterior ridge sharp and well 

 defined; epidermis shining, sometimes wrinkled looped, and painted 

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

 beaks flattened ofl' 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 branchiae more or less free from the abdominal sac ; mar- 

 supium 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 jpapillse. 



(Group of Plagiola elegans.) 



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

 extending from the beaks to the hinder i3oint 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, \). 58. — * H. and 

 A. Adams, Gen. Rec. Moll., II, 1857, p. 495. — * Chenu, 111. Conch., 1858, pi. xv, 

 figs. 3, 3a, 3&; * 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. 



