Description of a Neiu Species of Thracia. 



145 



Art. XIII. — Description of a New Species of Thracia; by 0. B. 

 Adams, Prof. Ghem. and Nat. Hist. Middlebury College. 



Thracia ineq,ualis. 



T, testa fragili, per-inequilaterali, per-inequivalvi, irregulariter 

 striata, postice truncata ; valva sinistra subplaniilata ; altera per- 

 convexa ; callo nymphali cochleariformi, anteriiis elongate ; ossi- 

 culo lunato, semicirculari. 



Shell white, very thin, before broadly and behind narrowly 

 truncate, very inequilateral and inequi valve, much deflected to the 

 left anteriorly ; with the striae of growth unequal, numerous and 

 crowded at the extremities, where, under a magnifier, the surface 

 appears shagreened by minute wrinkles of the striae ; epidermis 

 very thin, brownish, thicker at the extremities ; left valve nearly 

 flat, with five obtuse angles radiating from the beak ; right valve 

 much larger and very convex, emarginate in the whole of the 

 posterior truncation, with a groove and elevated umbonial angle 

 defining the areolar region, its inferior margin sinuous; heaks 

 small, pointed, lamelliform, the right one moderately excavated 

 for the reception of the other ; nymphceal callosities spoon-shaped, 

 very much produced forwards and inwards ; ossiculum semicir- 

 cular and lunate, with an impression on the centre of each side, 

 but much deeper on one side, situated between the spoon-shaped 

 apophyses and the dorsal margin. 



Dime7isions.' — Length 1.2 inch. ; height .75 inch j width .45 

 inch; length of ossiculum .1 inch.* 



Cabinet of Middlebury College. 



Habitat, Gulf of Mexico. 



Remarks. — A single specimen of this interesting species was 

 presented to the cabinet of this college by the Rev. Wm. T. Ham- 

 ilton, of Mobile, Ala. It is remarkable for the disparity of the 

 valves, the irregularity of its form, and the sharp lamelliform beaks. 



* The ossiculum is enlarged about 2^ linear diameters. 

 Vol. SLiii, No. 1. —April- June, 1842. 19 



