NO. 1205. SYNOPSIS OF THE NAIADES— SIMPSON. 615 



irregular concentric ridges ; epidermis beautifully painted by undulated, 

 radiating, broken hair lines or fine maculatious; hinge plate wide and 

 flat; pseudocardinals triangular, small and low, ragged; laterals low, 

 short, club-shaped; cavity of the beaks deep and compressed, dorsal 

 muscle scars on the under side of the hinge shelf; adductor scars small; 

 front part of the shell very thick, suddenly becoming thinner at the row 

 of humps; male and female shells much alike. 



Animal with the inner branchiae much the larger, curved below, free 

 from the abdominal sac; marsupium occupying the base of nearly the 

 whole outer branchia) in numerous rather indistinctly marked ovisacs, 

 bases of the ovisacs slightly rounded; ova very minute; palpi small, 

 curved; branchial opening very large, extending one-third of the way 

 along the base, fringed with many brown papilla?; anal opening very 

 large, finely crenulated. 



tDROMUS DROMUS Lea. 



* Unio dromus Lea, Tr. Am. Phil. Soc, V, 1834, p. 70, pi. x, fig. 29; * Obs., 1, 1834, 



p. 182, pi. X, fig. 29. — " Ferussac, Guer. Mag., 1835, p. 29. — "^ Conrad, Monog., 

 X, 1838, p. 84, pl.XLVi, fig. 2.— *Hanjley, Test. Moll., 1842, p. 181; * Biv. 

 Shells, 1843, p. 181, pi. xxiii, fig. 25. — * Catlow and Eeeve, Conch. Nom., 

 1845, p. 58.— * Conrad, Pr. Ac. N. Sci. Phila., VI, 1853, p. 248.— *H. and A. 

 Adams, Gen. Eec.Moll., II, 1857, p. 496.— *Kuster, Conch. Cab. Unio, 1861, 

 p. 172, pi. Liii, figs. 3, 4.—* Reeve, Conch. Icon., XVI, 1864, pi. viii, fig. 29.— 

 * B. H. Wright, Check List, 1888.—* P.5stel, Conch. Sam., Ill, 1890, p. 15L 



* Margarita ( Unio) dromus Lea, Syn., 1836, p. 16; 1838, p. 16. 

 *Cyprogenia dromus Agassiz, Arch, flir Naturg., I, 1850, p. 48. 

 * Margaron ( Unio) dromus Lea, Syn., 1852, p. 23; 1870, p. 34. 



Tennessee and Cumberland Eiver systems. 



t DROMUS CAPERATUS. Lea.' 



* Unio caperatus Lea, Pr. Am. Phil. Soc, IV, 1845, p. 164; " Tr. Am. Phil. Soc, X, 



1848, p. 75, pi. V, fig. 14; ^ Obs., IV, 1848, p. 75, pi. v, fig. 14.— * H. and A. 

 Adams, Gen. Eec Moll., II, 1857, p. 496.—* Reeve, Conch. Icon,, XVI, 1864, 

 pi. v, fig. 19.— *B. H. Wright, Check List, 1888.—* P^tel, Conch. Sam., Ill, 

 1890, p. 147. 

 *Margaron ( Unio) caperatus Lea, Syn., 1852, p. 22; 1870, p. 34. 



* Unio ahacoides Haldeman,- Pr. Ac N. Sci. Phila., Ill, 1846, p. 75; * Am. Jl. of Sci., 



II, 1846 (September), p. 274. 



Tennessee Eiver system. 



DIAGEN^^. 



Male and female shells alike; embryos contained in the outer gills in 

 short ovisacs which run crosswise of the branchiee, and are dischari-ed 

 entire into the water. 



' Generally this form is more compressed and less humped than D. dromus, bnt I 

 think it is probably only a variety of the latter. 



2 Haldeman only gave a brief description of his species, and it has never been 

 figured. According to Lea it equals his U, caperatus, and I believe he is correct. 



