NO. 1205. S YNO PSTS OF THE NA I A DES— SIMPSON. 757 



radial, rougbeued; laterals short, heavy, nacre white, brilliantly irides 

 cent posteriorly; beak cavities shallow. 



Animal apparently having ovisacs in pairs which are slightly wavy 

 and lirate at the base; gills rather large, semicircular, inner much the 

 larger, partly free from the abdominal sac; mantle thin, thickened at 

 edge, and bordered with a dark line.^ 



t PLEUROBEMA SHOWALTERII Lea. 



* Unio shoivalterii Lea, Pr. Ac. N. Sci. Pliila., IV, 1860, p. 307; * Jl. Ac. N. Sci. 



Phila., V, 1862, p. 73, pi. viii, fig. 223 ; Obs., VIII, 1862, p. 77, pi. viii, fig. 223.— 

 *SowERBY, Couch. Icon., XVI, 1868, pi. lxxxi, fig. 426.— *B. H. Wright, 

 Check List, 1888.—* P.etel, Conch. Sam., Ill, 1890, p.l67. 

 * Margaron {Unio) sTiowalterii'L^A., Syn., 1870, p. 55. 



Coosa Eiver, Alabama. 



(Group of Pleurohema nux.) 



Shell oval, inflated, moderately solid, with a low posterior ridge, 

 swollen at the post-basal part; posterior end pointed at the termi- 

 nation of the posterior ridge; beaks full, rather high, considerably 

 removed from the anterior end; epidermis pale to dark brown, rest 

 lines very distinct; pseudocardinals small, stumpy, radiate, rough, 

 laterals straight; nacre brilliantly iridescent posteriorly; front part of 

 shell heavy, suddenly becoming thinner behind. 



Animal unknown. 



t PLEUROBEMA VERA Lea. 



*Unio verus Lea, Pr. Ac. N. Sci. Phila., V, 1860, p. 140; *J1. Ac. N. Sci. Phila., V, 

 1862, p. 83, pi. XI, fig. 231; * Obs., VIII, 1862, p. 87, pi. xi, fig. 231.— *B.IL 

 Wright, Check List, 1888. 



* Margaron ( Unio) verus Lea, Syn., 1870, p. 38. 



Black Warrior and Cahawba rivers, Alabama. 



t PLEUROBEMA HAGLERI Frierson. 

 '* Unio (Pleurohema) Jiagleri Frierson, Nautilus, XIII, 1900, p. 109, pi. ii. 

 North Eiver, Alabama, near Tyner. 



t PLEUROBEMA RUBELLA Conrad. 



* Uriio ruhellus Conrad, New F. W. Shells, 1834, p. 38, pi. vi, fig. 2, p. 71. — *FEKrs- 



SAC, Guer.Mag., 1835, p. 29.— *Moller, Syn. Nov. Gen., 1836, p. 205.— *Han- 

 LEY, Test. Moll., 1842, p. 201 ; *Biv. Shells, 1843, p. 201.— *Chenu, Bib. Conch., 

 Istser., Ill, 1845, p. 20, pi. ii, fig. 2.— *CATLOWand Keeve, Conch. Norn., 1845, 

 p. 63.— *CoNEAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 257.— *H. and A. Adams, 

 Gen. Eec. Moll., II, 1857, p. 492.— *B. H. Wright, Check List, 1888.— *P.etel, 

 Conch. Sam., Ill, 1890, p. 166. 



' The single species which I place in this group is quite variable. Some specimens 

 approach Quadrnla solida and trigona in general shape, while others are more like 

 / leiirobema irrasa and troscheliana. I judge from the character of the gills that the 

 iiiiirsupium is confined to the outer pair. 



