.Shells found in Essex Counlij. 5.3 



by minute observers. Found occasionally at Lynn. Length 

 about half an inch. 



Described by Say, in Journ. Acad. Nat. Sc. Phil., vol. ii., 

 p. 318. 



Cabinet of the Society. 



Obs. I have found it more abundant on the shores of Maine 

 than in this vicinity. 



PETRICOLA. Latin, Inhabiting rocks. 



FORNICATA. Latin, fornix, a furnace. 



Arch ribbed stone borer. 



Shell transversely lengthened out, posterior side very short ; 

 anterior gaping a little. Across the valves are numerous lines ; 

 those nearest the posterior, furnished with ribs or arches, 

 (costae.) Teeth two, on each valve ; one of which is nearly 

 divided to its base, giving the appearance with the other of there 

 being three. Color white ; texture delicate, nearly smooth 

 within ; excepting the deep grooves towards the posterior end. 



Described very minutely by Say, in Journ. Acad. Nat. Sc. 

 Phil., vol. ii., page 219. 



SYN. PETRICOLA PHOLADIFORMIS, Lamarck, and figured, as 

 such in Say's Am. Conch.", pi. 60, fig. 1. A poor figure in 

 Brown's Zool. Text Book, pi. xc. fig. 17. 



Very abundant on the sandy beaches of Essex County, and 

 boring in great quantities into the hard blue clay, at low water 

 mark, on Phillips' beach, Lynn. 



This beautiful native Mollusk will present to the attentive ob- 

 server of Nature, an interesting subject for study. Two living 

 specimens, one in my possession, and the other in possession of 

 a friend, lived for several weeks in apparent health, by the occa- 

 sional change of sea-water. With a little sand on the bottom of 

 the vessel in which it was placed ; my specimen, would ele- 

 vate or depress itself by the muscular action of its body, ex- 

 tended from the edges of the valves. The other was not furn- 

 ished with sand. Two curious tubes similar to those of the 

 Pholades, were extended from the beaked end, the aperture of 

 which served for the imbibition and rejection of water, a constant 

 current of which was kept up when these tubes were beneath the 



