144 PHOLAS. PIDDOCK. 



gape when closed, rough with spinous excrescences, which 

 decrease towards the smaller end where it is nearly smooth : 

 hinge reflected, without cells, with a single oblong plate at 

 the back, but none below the hinge ; and on the internal 

 margin of the hinge above the insertion of the tooth is a 

 rounded knob or protuberance in each valve : length three 

 quarters of an inch ; breadth an inch and a half. 

 Burrowed in sandstone and clay. v. v. 



3. Pholas Candida. White Plddock. Fig. 70. 



Lister, pi. 435. f. 278 Pennant, pi. 42. f. 2 Donovan, 

 pi. 132 Wood, pi. 14. f. 3, 4 Dorset Cat. pi. 1. f. 12. 



Shell very thin, oblong, white or yellowish-white, trans- 

 parent, rounded and not sloping to a beak at the broader 

 end where it is nearly closed when shut, rough with points 

 all over except close to the cartilage on the back, with se- 

 veral rows of prickles on the broad end from the hinge to 

 the margin : hinge smooth, white, reflected, without cells, 

 with a single oblong somewhat curved strong plate on the 

 back, but none connecting the valves below the hinge ; 

 teeth slender, curved, and in one valve only there is an ad- 

 ditional tooth placed upon the interior margin of the hinge, 

 which is pointed, curved towards the cartilage and leaning 

 towards the elongated end, locking into a groove of the 

 opposite valve : length three quarters of an inch ; breadth 

 an inch and a half. v. v. 



Masses of rock, taken at the mouth of the river just be- 

 low the town of Teignmouth in Devonshire, and inclosing 

 'vast numbers of these three species indiscriminately and 

 collectively, are now before us while we are describing 

 them. The writers who have succeeded Montagu do not 

 seem to have well understood their peculiar differences, or 

 to have distinctly discriminated them. The manner of their 

 reticulation, as adopted by Linne, is by no means sufficiently 

 clear to form intelligible specific distinction. Ph. Dactylus 

 is at once known by the cells at the back of the hinge, a 

 circumstance mentioned by Mr. Wood only, and when in a 

 perfect state by the four dorsal valves, two of which cover 

 the cells, the triangular one which supports these two, and 

 the narrow elongated one beneath this last. Ph. parva, 

 which iu its outline, large frontal gape, and elongated beak, 



much 



