FAMILY UNIONIDE — ANODON. 199 
GENUS ANODON. Bruguieéres. 
Animal as in the two preceding genera. Shell generally thin; hinge toothless; all the other 
characters of the two preceding genera. 
ANODON UNADILLA. 
PLATE XV. FIG. 228. 
(CABINET OF DR. BUDD.) 
Description of the adult shell, solid, concentrically rugose, (more particularly on the posterior 
portion), transversely subelliptical, kidney-shaped, inflated, inequilateral. Beaks large, elevated, 
contiguous, very prominent, anterior to the centre of the shell: greatest diameter near the centre 
of the shell. ‘Hinge-margin shghtly arched, nearly straight: upper posterior margin sloping 
to the regularly rounded posterior margin; basal margin widely arcuated and compressed 
on the side ; anterior margin broadly and regularly rounded. Within, the cavity is capacious ; 
in the beaks, deep and wide, with a crescent-shaped deep cicatrix far within: palleal impres- 
sion very distinct. Anterior cicatrices confluent ; posterior distinct, the upper very small, and 
placed immediately under the end of the hinge-ligament; dorsal cicatrices five, very conspi- 
cuous, small, and arranged in a regular series anterior to the cavity of the beak. 
Color. Epidermis dark brown, passing into dark olive green on the basal margin ; beaks 
yellowish brown: within, salmon-color, brightest within the limits of the palleal impression ; 
margin bluish white. 
Vertical axis, 20; transverse ditto, 3°5. Diameter, 1-5. 
This species is an exception to the old generic character, as it is remarkably stout and solid. 
It was obtained by Dr. C. H. Stillman, from Unadilla river, Otsego county, a tributary of the 
Susquehannah. In its general outline it resembles A. cylindracea of Lea, but is at once 
distinguished by its solidity and greater inflation, and the situation and prominence of its 
beaks; the palleal impression, in our specimens, may be traced through the posterior cica- 
trices. In the smaller specimens, the beaks are distinctly undulated ; the epidermis is darker, 
and the nacre is of a deeper salmon-color : the palleal impression in all may be traced through 
the posterior muscular impressions. 
