208 
Unio Tugoms, Barnes. SilUman’s Journ., vol. 6, p. 126. Hil- 
dreth, Silliman’s Journ., vol. 14, p. 282. 
Trans. Amer. Phios. Soc., JV. S., vol. 3 
Besc. Shell narrowed, compressed and thin before • short, ob- 
tuse, rounded and wider behind : beaks slightly elevated ; liga- 
ment more elevated than the beaks ; hinge margin compressed, 
carinate ; basal margin falcate, emarginate, and compressed ; an- 
terior margin subangulate ; anterior dorsal margin subtruncate, 
nearly straight; anterior basal margin projecting; epidermis dark 
brown, under the epidermis pearly white ; surface rough and scaly, 
wrinkled transversely and waved longitudinally, having distinct 
irregular transversely compressed tubercles ; a broad nodulus, ele- 
vated, somewhat double ridge extending from the beaks to the 
anterior basal edge, and projecting on that part; a broad furrow or 
wave behind the ridge ending in the emarginate basal edge, and a 
furrow before separating the anterior hinge and anterior dorsal 
margin ; cardinal teeth sulcated ; lateral tooth striated, rough, and 
in the left valve somewhat double ; posterior muscular impression 
deep and partly rough ; cavity of the beaks angular, compressed 
and directed backward under the cardinal tooth; naker pearly 
white, and on the fore part iridescent. 
Ohs. The above is Barnes’ description of this strongly marked, 
common species. It is an inhabitant of the Ohio and its tributa- 
ries, and approximates, by its varieties to some of the varieties of 
IT. huUatus, Baf. Barnes compares it with the TJ. verrucosus, 
Raf., to which, however, it has but a remote affinity. I have re- 
ceived specimens from Dr. Hildreth of Marietta and Mr. Barabino 
of New Orleans. The impressions of the plate, with Barnes’ name 
of rugosus, were colored before I received the Monograph of the 
Bivalve shells of the Ohio,” the faithful translation^of which, Mr. 
Poulson presented to me. PI. 53, 
Planorbis.— -Shell univalve, thin, fragile, discoidal or revolving 
in the same horizontal plane ; concave above and beneath, the spire, 
being impressed ; aperture rounded-ovate, entire at base, the labia 
interrupted by the convexity of the penultimate volution ; labrum 
simple ; operculum none. Animal depressed, spiral sinistral ; foot 
rounded, small ; tentacula two, long, slender, contractile ; eyes at 
the inner base of the tentacula ; mouth somewhat exertile, armed 
and 4. 
