Pholas. MOLLUSCA. PHOLADiE. 457 



555. P. tubercidatus. — Shell open at the anterior end, with a 

 rough tubercle on the margin above the teeth, and a single 

 oval calcareous plate at the hinge extending to the anteal ex- 

 tremity. 



Turt. Biv. Brit. v. t. i. f. 7, 8 Torbay. 



Length three-quarters of an inch, breadth an inch and a half; white ; front 

 of the shell slightly elongated into a beak ; anterior compartment with rough 

 ribs, which gradually disappear towards the retral truncated extremity. 



556. P. conoides. — Transversely elongated, anteal division 



short, tumid, rounded, the retral division produced and subcom- 



pressed. 



Parsons, Phil. Trans. 1765, i. t. 1. — P. striatus, Linn. Syst. i. 1111 



P. nanus, Pult. Dorset. 27. — P. stri. Don. Brit. Shells, t. cxvii. Moid. 

 Test. Brit. 26. Turt. Biv. Brit. 11 — In ship planks. 



Length half an inch, breadth an inch ; ridges in the anteal compartment 

 crowded, rough ; in the retral wider and smoother, well marked along the 

 furrow ; nearly closed retrally ; when young, very open anteally, and beaked, 

 but filling up with smoother shell (like P. papyracea) towards maturity ; one 

 large rounded accessory plate over the hinge, behind which is a lengthened 

 one, and a third connecting the ventral margins of the shells ; a long slender 

 curved tooth in each valve. 



** The valves not divided by a groove. 



— 557. P. dactylus: — Conically transverse, with concentric, 

 waved, muricated ridges, having longitudinal grooves, most con- 

 spicuous anteally ; margin above the beaks reflected, circular, 

 with four accessory plates. 



P. striatus, 'List. Conch, t. ccccxxxiii. Anat. t. xix. f. 1 , 2 — P. dact. 

 Linn. Syst. i. 1110. Borl. Corn. 278. t. xxviii.-xxxi. Mont. Test. 

 Brit. 20. Turt. Biv. Brit. 8 — In rocks and submarine trees. 



Length sometimes 2 inches, and breadth 7 ; wide and open before ; slight- 

 ly compressed behind ; shell in front of the hinge produced into a kind of 

 beak, with the edge thin and reflected. 



— 558. P. parvus. — Shell open, and produced into a beak an- 

 teally, with a smooth tubercle on the margin above the teeth, 

 and a single accessorial valve at the hinge. 



Mont. Test. Brit. 22. t. i. f. 7, 8. Turt. Biv. Brit. 9 — Submarine wood 

 on the south coast of England. 

 Length fths, breadth 1^ inches ; transversely striated, with longitudinal 

 ridges anteally ; the anteal opening is oval, and the fold above the beaks des- 

 titute of cells. Montagu is inclined to consider this shell as the P. parvus of 

 Pennant, (Brit. Zool. iv. 77- t. xl. f. 13.) though it is not improbable that it 

 is related to the young of P. papyracea. 



559- P. candidus. — Shell nearly closed anteally; a tooth- 

 like process on the hinge ascending obliquely and retrally ; 

 margin above the hinge reflected, and covered with an elongated 

 accessorial plate. 



Concha Candida, List. An. Aug. 193. t. v. f. 39. Conch, t. ccccxxxv — P. 



