104 pholadidjE. 



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 Hypogcea 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. 



1. Pholas dac'tylus"*, Linne. 



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 with short papillae ; orifice of longer 

 tube margined with about a dozen fringed tentacles, besides as 

 many intermediate smaller ones which are ciliated on the 

 sides ; the excurrent tube has its orifice either j>lain or mar- 

 gined with a few short cirri ; the points of the siphonal ten- 

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

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

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



Shell elongated, somewhat obliquely twisted on the anterior 

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

 small prickles or vaulted scales, which are formed by the in- 

 tersection of slight longitudinal ribs and wavy transverse 

 striae ; these prickles extend over the greater part of the shell, 

 but they are much stronger and more crowded on the anterior 

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

 side, where they are altogether Wanting ; this latter part is 

 often coarsely and irregularly granular, as if from an imperfect 

 consolidation of the shell; the whole 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, widelv 



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

 S&ktvXos or dactylus of the ancients. 



