76 INVERTEBRATA OF MASSACHUSETTS. 



the longer side regularly rounded ; valves tumid, surface with 

 minute, concentric wrinkles, which, towards the base, enlarge 

 into obvious, sharp folds ; color a light-olive, with darker zones, 

 and a marginal border of yellowish ; within bluish or greenish ; 

 teeth well developed. Length i inch, height i inch, breadth 

 2^ i"ch. 



Found in streams in Bristol County, and in ditches in the Cam- 

 bridge meadows, in company with the last species, and probably 

 in all parts of the State. 



Here, again, we have a shell bearing a close resemblance to a trans- 

 atlantic species, the C. ohliqua of Lamarck, C. dmnica of some writ- 

 ers. The foreign shell, however, is somewhat longer, less inequilat- 

 eral, and more oval, and the wrinkles are somewhat more conspicuous. 

 The young shells of our species have the beaks more removed to- 

 wards the centre, and the short side more rounded, so as to be scarcely 

 distinguishable from the European species. In general appearance it 

 is very like Niicula tenuis. 



Genus ASTARTE, Sowerby. 



Shell rounded^ sub-equilaicrcti, comj^resscd, thick ; hinge with 

 two strong.^ diverging, cardinal teeth on one valve, and two very 

 unequal ones on the other, or only one large one; j^fflleal impres- 

 sion simyle; ligament exterior. 



Asta'rte castanea. 



Shell suh-orhieular , with prominent and nearly central beaks ; 

 lunule deeply excavated ; surface very slightly waved, covered loith 

 a chestnut-brown epidermis ; margin crenidated xoithin. 



Figure 44. 



State Coll., Nos. 205, 207. Soc. Cab., No. 1S06. 



Venus castunea, Say ; Journ. jicad. J\^al. Sc, iv. 5273. 



Astarte castanea, Say ; ^mer. Conch., pi. 1. Totten ; Sillirumis Journ , xx viii. f. 2. 



Crassina castanea, Lam. ; .An. sans Vert., vi. 258. 



Shell thick and ponderous, sub-orbicular, or sub-triangular, the 

 beaks nearly central, and much elevated, generally eroded ; the 

 areola in front of the beaks is ovate-lanceolate, short, broad, 

 deeply excavated, very smooth and darker colored ; posterior 



