196 NEW-YORK FAUNA — MOLLUSCA. 
GENUS ALASMODON. Say. 
Animal resembling that of Unio. Shell with a primary tooth on each side : no lateral tooth. 
ALASMODON RUGOSA. 
PLATE XIV. FIG. 226. 
(STATE COLLECTION.) 
Alasmodonta rugosa. Barnes, Am. Jour. Sc. Vol. 6, p. 278, pl. 13, fig. 21. 
Margarita (Margaritana) rugosa, Lea, ‘Trans, Am. Phil. Soc. Synopsis, p. 135. 
A. rugosa. Apams, Am. Jour. Sc. Vol. 40, p. 276. 
Description. Shell oblong-oval, moderately compressed, rather broader in front. Beaks 
slightly elevated, wrinkled, and, when decorticated, exibiting a waxen color beneath. Liga- 
ment external, and as high as the beaks. Anterior lunule distinct, with a slightly elevated 
ridge extending from the beaks to the anterior basal margin, which is very slightly contracted. 
Surface, towards the anterior margin, folded in a pinnate form: folds deeper above, some- 
what obsolete below; the ridge curved upward, and extending to the hinge and anterior mar- 
gins, indenting the edge and visible within. Teeth large, elevated, serrate, with a fold 
behind: cavity small. 
Color. Epidermis dark olive and of a silken lustre, frequently with pale narrow radiations ; 
within bluish white, salmon-colored towards the cavity of the beaks, faintly iridescent. 
Vertical axis, 2°0 — 2°9; transverse ditto, 3'1 - 3°7. 
This very beautiful and distinct species figured above, was obtained from Oswego river. 
In others, procured from Oak-orchard creek, Orleans county, the rugosities were not so pro- 
minent, giving place to concentric scales; nor was the silken lustre of the epidermis so 
obvious. In these latter, too, the color within was more uniformly of a bluish purple. 
ALASMODON MARGINATA. 
PLATE XIV. FIG. 225. 
(STATE COLLECTION.) 
Alasmodonta marginata. Say, Nich. Ency. pl. 3, fig. 4. 
Monodonta id. Ip. lb. Ed. prior. 
A. id. Say, Journ, Acad. Nat. Se. Vol. 1, p. 459. 
A. id. Barnes, Am. Journ. Sc. Vol. 6, p. 279. 
Margaritana marginata. Lea, Trans. Am. Phil. Soc. Vol 6, p- 135. 
A, id. Goutp, Invertebrata of Mass. p. 116, fig. 77. 
Description. Shell small and thin, oblong, suboval, widely gaping behind. Beaks rather 
small, but somewhat elevated, with three or four concentric undulations. Hinge-margin 
