ARCACEA. MOLLUSCA. NUCULA. 97 



NUCULA THRACIiEFORMIS. 



Shell kidney-shaped, inequilateral, covered with a dark olive- 

 green epidermis ; a rib-like wave passes from the beaks to the pos- 

 terior-inferior angle ; gaping at both ends. 



Figure GG. 



State Coll., No. 183. Soc. Cab., No. 2318. 



Nucula thraciasformis, Storer ; Bost. Journ. JVat. Hist., ii. 122. (wood-cut.) 

 Shell oblong-ovate, or rather kidney-shaped, somewhat pointed 

 before, broadest and truncated behind, thin ; gaping at both ends ; 

 inequilateral ; the beaks considerably elevated, pointed, inclined 

 backwards, and touching each other, are situated near the anterior 

 third of the shell ; an obtuse, rib-like wave passes obliquely over 

 the shell from the beaks to the posterior third of the basal margin, 

 dividing the surface of the shell into two unequal triangles ; the 

 outline of the anterior triangle is regularly curved, excepting a 

 shallow, lengthened notch between the centre of the base and the 

 wave ; the upper margin of the other triangle is nearly direct, a 

 little upturned or beaked, and its edge is compressed into a sharp 

 crest, the posterior margin moderately rounded, joining above 

 and below with an abrupt curve of a truncated appearance ; the 

 anterior portion is inflated, and the epidermis of a dusky green ; 

 the posterior portion is compressed, has one or two faint waves 

 or radiations, and the epidermis is of a lighter yellowish-green, 

 minutely wrinkled ; surface coarsely marked with lines of growth, 

 and covered with a sooty powder, which easily rubs off and leaves 

 a glossy black. Hinge with a very large, spoon-shaped cavity, 

 and on each side of it are about twelve teeth, each one folded from 

 the centre to an angle of 45*^ ; cavity of the beaks very ca- 

 pacious ; interior polished white, impressions faint, the palleal one 

 with a deep sinus. Length 2| inches, height m inch, breadth 

 ly^ inch. 



First taken by Dr. Storer from the stomachs of Pleuronectes 

 dentata, or sand-dab, cRught off Race Point, in December, 1837. 

 In that winter a dozen or more specimens were taken from the 

 same species of fish, and from the same locality ; but last winter 

 they were sought for without success. 



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