﻿492 ALASMIDONTA 



\ ar. kathcriiifc (Lea). 



Shell much smaller than the ordinary manifestation of the 

 species, irregularly elliptical or ohovate and wanting the dor- 

 sal wing". 'T\\Q epidermis is smoky-hrown ; the beaks in the 

 specimens 1 have seen are so badly eroded that I cannot form 

 any idea of their sculi)ture. It seems to l^e the arctic manifesta- 

 tion of the species, wdiich is so common in western rivers. 



Length 90, height 62, diam. 23 mm. 



Type locality, Lake Superior. Also Lake \\'innipeg ; Sagi- 

 naw Bay, Michigan. 

 Unio kathcriiKc Lea. Syn., 1838. p. 35 ; Tr. Am. Phil. Soc, VL 



1839, p. 143- 

 Symphynoia complanata var. kathcrincc Simpson, Svn., 1900, 



"p. 666. 



One of the largest and most ponderous of ihe Naiades. The 

 hinge is more solid and the form of the shell is more rounded 

 than the other species I have placed in Symphynota. But oc- 

 casional specimens have hinges much like that of S. costata 

 and shells drawn out so that they approach S. coiiiprcssa in 

 form. 



Genus ALASMTDONTA Say. 1818. 



Monodonla S.\\\ Nich. b"nc., U, 1817. 



Alasmidonta Say, Jl. Ac. N. Sci. Phila., L 1818, p. 459. — Ort- 



MANN, Ann. Car. Mus., VIH, 1912, p. 294. 

 Alasmodnnta Say, Nich. Enc, 3d ed., I\', 1819. 

 Uniopsis Swainsox. Tr. on Alal. 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 double-looped bars : epidermis 

 rayed, shining ; hinge with two pseudocardinals in the left 

 valve and one in the right : laterals wanting or imperfect ; 

 cavity of the beaks deej) : dorsal scars under the hinge plate; 

 nacre bluish. 



Animal with the marsupium occupying the entire outer gills ; 

 .^^ills roimded below, inner much the larger, united to the ab- 

 dominal sac, or free ; mantle generally having square spots on 



