146 PHOLAS. PIDDOCK. 



air also seems to be occasionally necessary to this process, 

 as they are always found in situations which are left dry 

 for a short period by the recess of the lowest tides, its oxy- 

 gene perhaps serving by its union with this secretion to 

 form a phosphorous acid. In confirmation of this belief we 

 have affixed them, when fresh taken, to a smooth piece of 

 the same rock, by the frontal gape, occasionally moistening 

 them with sea water ; and in a few days have found, that at 

 the place of contact an evident waste of substance had been 

 made by the decomposition of the lime, and a deposition 

 of sand in the finest grains. It may reasonably be supposed 

 that all the borers of rocks and wood, even the Teredo, 

 act in this manner by their peculiar and appropriate sol- 

 vents. 



4. Pholas crispata. Curled Piddock. 



Lister, pi. 436. f. 279 Pennant, pi. 43. f. 2 Da Costa, 

 pi. 16. f. 4 Donovan, pi. 62 Wood, ph 15. f. 3, 4, and 5 

 Dorset Cat. pi. 3. f. 4. 



The young shell. 



Pholas Candida. Donovan, pi. 69. 



Shell strong, gibbous, somewhat oval, much rounded at 

 one end and narrower at the other, and very open at both, 

 whitish or rust-color, marked by a longitudinal furrow from 

 the hinge to the margin, which divides the shell into two 

 nearly equal parts ; one of which is smooth, except a few 

 transverse striae ; the other rough with strong transverse 

 undulate or indented raised scale-like folds , inside white, 

 with a longitudinal rib in the middle answering to the furrow 

 on. the outside : hinge smooth, white, forming a furrow on 

 the back at the anterior end which is obliquely truncate : 

 teeth long, flat, much curved : length nearly two inches , 

 breadth almost three. 



We have never been able to discover this species in its 

 natural habitation, nor have we met with any one who ever 

 had : the dorsal valve has consequently not been described 

 by any writer. It is said to be imbedded in hard clay and 

 limestone. 'Maton and Rackett, and Mr. Wood, have er- 

 roneously described the groove or furrow which divides the 

 shell into two parts, extending from the binge to the mar- 

 gin, as a transverse one. v. m. 



5. Pholas 



