NO. 1205. SYNOPSIS OF THE NAIADES— SIMPSON. 589 



portion of the shell plicately or nodulously wrinkled; epidermis smooth 

 and bright, variegated with broken green rays and blotches; beak sculp- 

 ture consisting of rather fine, subi)ara]lel, often broken ridges in two 

 loops, the anterior rouuded, the posterior somewhat angled, occasion- 

 ally broken up into zigzags; ^ pseudocardinals small, stumpy and some- 

 what roughened; laterals rather short, slightly curved and club-shaped, 

 remote; dorsal cicatrices few, placed under the hinge just behind the 

 beaks; anterior cicatrices rather deep; posterior cicatrices rounded, 

 large, and well impressed; anterior part of shell somewhat thickened; 

 female shell slightly swollen just behind the middle of the base. 



Animal with the inner gills wholly or in part free from the abdominal 

 sac; marsupium occupying the central posterior part of the outer gills, 

 sometimes extending nearly theii* whole length, consisting of few to 

 many rather large, irregular ovisacs, which are not so distinctly 

 marked out as in Lampsilis, but which have rounded bases; mantle 

 much thickened on its lower edge, which is dark colored and sometimes 

 papillous. 



(Group of Medionidus conr adieus.) 



Shell small, usually with a well-defined posterior ridge; posterior end 

 and sometimes the greater part of the shell slightly wrinkled or nodu- 

 lous; epidermis rather smooth, painted with rays broken into irregular 

 arrow-head markings or blotches; pseudocardinals rather small and 

 imperfectly developed; laterals of left valve separated by a narrow, 

 shallow furrow; nacre greenish, purplish, or bluish. The male shell is 

 often decidedly arcuate; that of the female is swollen at or behind the 

 center of the base. Animal having the characters of the genus. 



t MEDIONIDUS CONRADICUS Lea. 



* Unio conradicus Lea, Tr. Am. Phil. Soc, VI, 1834, p. 63, pi. ix, fig. 23 ; *0b8., I, 



1834, p. 175, pi. IX, fig. 23. — " Ferussac, Gnerin. Mag., 1835, p. 29. — *" Hanley, 

 Test. Moll., 1842, p. 176; * Biv. Shells, 1843, p. 176, pi. xxiii, fig. 22.—* Catlow 

 and Reeve, Conch. Nom., 1845, p. 57. — "' Conrad, Pr. Ac. N. Sci. Phila., VI, 

 1853, p. 247.—' H. and A. Adams, Gen. Eec. Moll., II, 1857, p. 497.— *Kuster, 

 Conch. Cab. Unio, 1861, p. 179, pi. lvi, fig. 5. — * Sowerby, Couch. Icon., 

 XVI, 1866, pi. Liv, fig. 278.—* PzEtel, Conch. Sam., Ill, 1890, p. 148. 



* Margarita ( Unio) conradicus Lea, Syn., 1836, p. 13; 1838, p. 14. 



* Margaron ( Unio) conradicus Lea, Syn., 1852, p. 21. 



* Unio conradius Conrad, Monog., X, 1838, p. 87, pi. xlvii, fig. 3. 



* Margaron ( Unio) conradiauus Lea, Syn., 1870, p. 32. 



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



Tennessee River drainage; Cahawba River, Alabama, and probably 

 the entire Alabama River system. 



'The beaks in all the specimens of Unio suhtentus that I have examined were too 

 badly eroded to make out the character of the sculpture with certainty. In a gen- 

 eral way they seemed to be much like those of the Conradicus group, only coarser. 



