198 NEW-YORK FAUNA — MOLLCSCA. 



Alasmodon undulata. 



PLATE XV. FIG. 227. 



Alasmodonta undulata. Sav, Nich. Eneyl. Vol. 4, pi. 3, fig. 3. 



A. id. Id, Journ. Acad. Nat. Sciences, Vol. 1, p. 459. 



A. Jd, Barnes, Amer. Jour. Science, Vol. 6, p. 279. 



Margaritana'^.id. Lea, Trans. Am. Phil. Soc. Vol. 6, p. 135. 



A. id, Gould, Invertebrata of Mass, p. 115, fig. 76. 



Description. Shell moderately thin, much inflated, dilated and then attenuated in front, 

 regularly rounded behind, widely gaping. Beaks prominent, contiguous, often decorticated, 

 with four or five large obtuse distant concentric undulations ; these are, however, sometimes 

 indistinct : basal margin regularly curved. Surface much undulated by the incremental lines. 

 Hinge supported on a very strong rib. Tooth in the right valve double, crenate ; the anterior 

 erect, prominent, conical : in the other valve, the tooth is occasionally bifid. 



Color. Epidermis green or olivaceous, with numerous dark green radiations of unequal 

 breadth : within salmon-colored and bluish white ; iridescent on the anterior portion. 



Vertical axis, 1"0-1*3; transverse ditto, l"8-2'2. 



Found at Norman's kill in Albany county, Champlain, &c, 



Alasmodon corrugata. 



PLATE XXIV. FIG. 259. 



(CAB. LYCEUM NAT. HIST.) 



Description. Shell thin, ovate, rather tumid, not gaping. Beaks prominent, often eroded, 

 with one or two undulations. Ridge from the beaks posteriorly rounded, but prominent, and 

 forming a distinct area : within this area is another, bounded by two lines forming an ellipsis ; 

 from the anterior portion of this line, but reaching the ridge as we proceed posteriorly, arise 

 from fourteen to sixteen rounded elevated ridges, running obliquely upwards and backwards, 

 and strongly impressed on the inner surface. Tooth in one valve prominent, trifid ; in the 

 other, but slightly elevated and indistinct. Cavity of the beaks large and capacious. 



Color. Epidermis shining olive-green, and produced on the sides beyond the margin, olive- 

 brown on the beaks ; valves with faint radiating striae of a darker green, more distinct towards 

 the basal margin : within, violet in the cavity of the beaks, chalky on the margin. 



Vertical axis, l-O; transverse ditto, 1"8. Diameter, 0"75. 



I am indebted for this beautiful species to Mr, I, Cozzens, who obtained it from the Passaic 

 and its tributaries originating in the State of New- York, In many particulars it is allied to 

 A. marginata ; but the closed shell and trifid tooth, together with other obvious differences, 

 would seem to indicate the propriety of considering it as a new species. 



