666 PROCEEDINGS OF THE NATIONAL MUSEUM. 



^Margarita {Margaritana) complanata Lea, Syn., 1836, p. 43; 1838, p. 26. 



""Unio complanata Hanley, Test. Moll., 1842, p. 210; "^ Biv. Sheila, 1843, p. 210, pi. 



XXI, fig. 9. 

 '^Coviplavaria complanata Conrad, Pr. Ac. N. Sci. Pbila., VI, 1853, p. 261. 

 *Baphia c6mi)lanata H. and A. Adams, Gen. Rec. Moll., II, 1857, p. 500. 

 ^Margaraiina complanata Calkins, Pr. Ottawa Acad., 1874, p. 46. — *B. H. Wright, 



Check List, 1888.—* P.etkl, Conch. Sam., Ill, 1890, p. 172. 

 ^Alasmodon complanatus Sowerby, Couch. Man., 1842, p. 61, fig. 140. — " Catlow 



and Reeve, Conch. Nom., 1845, p. 57. — * Kuster, Conch. Cab. Unio, 1861, p. 



199, pi. Lxv, fig. 1.—* Sowerby, Conch. Icon., XVI, 1866, pi. l, fig. 266. 

 Complanaria gigas Sowerby, Conch. Man., 1839, fig. 141, *; 1842, p. 115, tig. 141. 

 ""I Megadomus gigas Swainson, Tr. on Mai., 1840, pp. 265, 378. 



t SYMPHYNOTA COMPLANATA var. KATHERINiE Lea. 



Unio katherince Lea, Syn., 1838, p. 35 ; ' Tr. Am. Phil. Soc, VI, 1839, p. 143.— " Tro- 

 SCHEL, Arch, flir Nat., V, 1839, II, p. 237. 



Upper Mississippi drainage, as far south as Arkansas on the west; 

 Ohio Eiver system; upper St. Lawrence and its tributaries; north into 

 the Mackenzie Eiver. 



Genus ALASMIDONTA Say, 1818. 



(Type, Monodonta undulata Say.)- 



Monodonta Say, Nich. Enc, II, 1816. 

 Alasmidonta Say, Jl. Ac. N. Sci. Phila., I, 1818, p. 459. 

 Alasmodonta Say, Nich. Enc, 3d ed., IV, 1819. 

 Alasmodon Swainson, Tr. on Mai., 1840, p. 382. 

 Uniopsis Swainson, Tr. on Mai., 1840, p. 382. 



Shell generally rhomboid, inflated, with a well -developed posterior 

 ridge, which ends in a point behind when it is single or a biangulation 

 when double; beaks full and high, with coarse, concentric or slightly 

 doubly looped bars; epidermis rayed, shining; hinge with two pseudo- 

 cardinals in the left valve and one in the right; laterals wantiug or 

 imperfect; cavity of the beaks deep; dorsal scars under the hinge 

 plate; nacre bluish. 



Animal with the marsupium occupying the entire outer gills; gills 

 rounded below, inner much the larger, united to the abdominal sac, or 

 free; mantle generally having square spots on the posterior border; 

 branchial oi^ening papillose; anal opening smooth or crenulate. 



Subgenus ALASMIDONTA Say, 1818. 

 (Type, Monodonta undulata Say.) 



Shell ovate rhomboid, solid, inflated, shining, with very strong, gen- 

 erally concentric beak sculpture; pseudocardinals solid, stumpy, some 



' This is probably the small, peculiar boreal form of this species, which appears 

 very different from the type. 



2 Changed by Say afterwards to Alasmidonta undulata as the name Monodonta was 

 preoccupied. For some reason Say later on called his genus Alasmodonta, 



