Pholas. MOLLUSCA. PHOLADyE. 457 



555. P. tuberculatus. — 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 disapjjear towards the retral truncated extremity. 



55Q. 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. Mont. 



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. J , 2. — P. dact. 

 Linn, ^y St. i. 1110. Borl. Corn. 278. t. xxviii.-xxxi. Mont. Tcsi. 

 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. 



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

 on the south coast of England. 

 Length fths, breadth 1 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. candidtis. — 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, Ang. 1'J3. t. v. f. 3D. Conch, t. ccccxxxv— P. 



