666 PROCEEDINGS OF THE NATIONAL MUSEUM. 



^Margarita (Margaritana) compJanata LEA, Syn., 1836, p. 43; 1838, p. 26. 



*rio complanata HANI.KY, Test. Moll., 1842, p. 210; * Biv. Shells, 1843, p. 210, pi. 



xxi, fig. 9. 



*Complanaria complanata CONRAD, Pr. Ac. N. Sci. Pbila., VI, 1853, p. 261. 

 "Sophia compJanata H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 500. 

 Margaratina complanata CALKINS, Pr. Ottawa Acad., 1874, p. 46. * B. H. WRIGHT, 



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

 "Alasmodmi complaj^atus SOWERBY, Couch. Mau., 1842, p. 61, fig. 140. * CATI.ONV 



and REEVE, Conch. Noin., 1845, p. 57. * KUSTEK, Conch. Cab. Unio, 1861, p. 



199, pi. i.xv, fig. 1.* SOWERBY, Conch. Icon., XVI, 1866, pi. L, fig. 266. 

 Complanaria yiyas 8 >WERBY, Couch. Man., 1839, fig. 141, * ; 1842, p. 115, tig. 141. 

 *? Megadomus ijigas SWAINSOX, Tr. on Mai,, 1840, pp. 2l>5. 37S. 



fSYMPHYNOTA COMPLANATA var. KATHERIN^E Lea. 



Unio katherina' LEA, Syn., 1838, p. '35 ; l Tr. Am. Phil. Soc., VI, 1839, p. 143.* TRO- 

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



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

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

 the Mackenzie River. 



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 biaiigulation 

 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 wanting or 

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

 plate; nacre bluish. 



Animal with the inarsupium 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 opening papillose; anal opening smooth or creuulate. 



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 



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

 very different from the type. 



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

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



