ARCACEA. MOLLUSCA. NUCULA. 105 



Nu'CULA te'nuis. 



Shell trapezoidal, thin, smooth, without radiating lines ; epider- 

 mis grass-green ; beaks prominent, placed anteriorly ; margin sim- 

 ple, teeth very few. 



Figure 64. 



State Coll., No. 287. Soc. Cab., No. 2340. 



Area tenuis, Montagu ; Test. Bril.y SiippL, 5G, pi. 29, f. 1. Pennant ; Brit. Zool., 



iv. 218. DiLLWYN ; Catal., 24G. Turton ; Conch. Diet., 1^. 

 Nucula tenuis, TiiRToN ; Brit. Biv., 177. Fleming; Brit. Anim., AQ2. 



This shell is very similar to the preceding, and would not at 

 once be distinguished from it. The following are some of the 

 essential difierences. The posterior margin, instead of running 

 straight to the posterior tip, runs about half the distance parallel 

 with the base, then forms an angle, and, by a broadly rounded 

 curve, joins the curve of the base ; the tip is, therefore, not 

 pointed as in N. proxima, and the angle of this side gives the shell 

 a four-sided, instead of a triangular figure, the greatest height be- 

 ing somewhat behind the beaks ; beaks prominent, curved for- 

 wards, and having a deep pit before them, not found in the other 

 species ; anterior margin forming as much as a right angle with the 

 posterior ; while in N. proxima we have rather less than a right 

 angle. The surface is smooth, glossy, grass-green, without any 

 radiating lines. Interior a silvery-white, but not pearly like the 

 other. The teeth are very long and slender, scarcely if at all 

 folded, and only about eight behind and four or five before the 

 beaks. The interior margin is always simple, but never so in the 

 smallest specimens of N. proxima. The shell is very thin, and 

 its breadth very small. Length j\ inch, height I inch, breadth 



Found in the stomachs of fishes, but much more sparingly than 

 the preceding. 



This shell, as far as I can recollect, is the one in the collection of the 



Academy of Natural Sciences at Philadelphia, marked " N. lucida, 



Blanding." It corresponds precisely with a specimen of Niicula 



tenuis sent me by Mr. Sowerby, and it is his opinion that they are 



identical. 



14 



