196 NEW-YOEK FAUNA — MOLLUSCA. 



I 



GENUS ALASMODON. Say. 



Animal resembling that of Unio. Shell with a primary tooth on each side : no lateral tooth. 



Alasmodon rugosa. 



PLATE XIV. FIG. 22fi. 



(STATE COLLECTION.) 



Alasmodonta nigosa. Barnes, Am. Jour. Sc. Vol. G, p. 278, pi. 13, fig. 21. 

 Margarita { Margaritana) rugosa, Lea, Trans. Am. Phil. Soc. Synopsis, p. 135. 

 A. rugosa. Adams, 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.) 



Alasmodon/a marginata. Say, Nich. Ency. pi. 3, fig. 4. 



Monodonta id. Id. lb. Ed. prior. 



A. id. Say, Journ. Acad. Nat. Sc. 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. Gould, Invertebrala 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 



