﻿49^ AI.ASMII'ONTA 



The names JJcmiodoii and llcinidoiita were applied by 

 Swainson to this group, but he used the first previously for 

 a division of the Helicidae and the second is merely feminine 

 of the first. He also used the name Hemidon, but whether it 

 was intended for the group of Alasmidonta calceolus or the 

 subfamily .llasiiiodoitfiiuc, 1 cannot detennine. 



Cirouj) of Alasmidonta calccoliis. 



Shell small, subsolijj, rhomboid, inflated, rayed but not shin- 

 ing ; beak sculpture varying from strong concentric bars to 

 irregular corrugations, sometimes faintly doubly looped, and 

 with fine radiating ridges in front and behind ; pseudocardinals 

 rather solid ; laterals very faint ; marsupium occupying the 

 whole of the outer gills, thick, i)ad-like; inner gills wholly or 

 partly free from the abdominal sac ; mantle bordered with 

 square, black spots. 



Alasmidonta cai.crolus (Lea). 



Shell rather small, convex to subinflated, usually decidedly 

 rhomboid, somewhat ine(|uilateral, subsolid ; beaks neither full 

 nor elevated, the sculpture varying from strong bars, which 

 run parallel with the growth lines to irregular, often doubly 

 looped, corrugations, generally with radial, raised threads in 

 front and behind ; posterior ridge usually high, rounded and 

 ending in a rounded point behind at the base of the shell, 

 rarely it ends just below the median line; surface with uneven 

 growth lines ; epidermis dull ashy or ashy-green with wavy 

 rays, sometimes the dark rays occupy most of the shell leav- 

 ing narrow light rays between; left valve with a blurred tooth 

 under the beak and a faint one in front ; right valve with one 

 tooth in front of the beak ; laterals blurred, often almost want- 

 ing ; nacre whitish, a little thicker in front. 



Length 50, height 30, diam. 22 mm. 



Length 36, height 22, diam. 15 mm. 



L^pper Mississippi drainage ; Ohio. Cumberland, and Ten- 

 nessee rivers; Lower and Middle St. Lawrence systems. 



Type locality. Ohio. 



