104 PHOLADID^E. 



rocks increases their hardness, and that the admixture 

 of organic matter with the mineral ingredient in the 

 shell diminishes the specific gravity of the latter. 



The animal is partly the Hypogaa of Poli. Three or 

 four genera have been proposed by Leach and Gray for 

 the shells of certain species. Pholas, being derived from 

 the Greek, is feminine. 



A. Shell oblong : hinge-plate furnished behind with a layer 

 of cells : dorsal shields 4, viz. 2 anterior, placed side by 

 side ; 1 cardinal, and complicated ; 1 posterior, and 

 elongated. Dactylina, Gray. 



U . CT2- 1. PHOLAS DAC'TYLUS*, Linne. (jfcfr) N'fctf 



P. dactylus, Linn. S. N. p. 1110; F. & H. i. p. 108, pi. iii. 



BODY oblong, whitish, sometimes tinged with blue or yellow : 

 tubes more or less covered witb short papillae ; orifice of longer 

 tube margined witb about a dozen fringed tentacles, besides as 

 many intermediate smaller ones which are ciliated on tbe 

 sides ; tbe excurrent tube bas its orifice either plain or mar- 

 gined with a few short cirri ; tbe points of tbe sipbonal ten- 

 tacles or cirri are brownish; outer sbeatb brown or of a 

 pepper-and-salt colour : foot rather obliquely fixed to tbe rest 

 of the body by a long, cylindrical, tbick, fleshy, white stalk. 



SHELL elongated, somewbat obliquely twisted on tbe anterior 

 side, moderately solid : sculpture, 40-50 longitudinal rows of 

 small prickles or vaulted scales, wbicb are formed by tbe in- 

 tersection ' of sligbt longitudinal ribs and wavy transverse 

 striae ; tbese prickles extend over tbe greater part of tbe shell, 

 but they are much stronger and more crowded on tbe anterior 

 side, and less so in front, and, especially, towards tbe posterior 

 side, where they are altogether wanting ; tbis latter part is 

 often coarsely and irregularly granular, as if from an imperfect 

 consolidation of tbe shell; the wbole surface also is closely 

 puckered : colour whitish : epidermis pale yellowish-brown, 

 more persistent at the edges : margins narrow, angular, and 

 more or less attenuated or beaked at the anterior end, widely 



* Shaped like a finger; formerly, but erroneously, supposed to be the 

 daKTvXos or dactylus of the ancients. 



