Identity of Pholadidea papyracea and Pholas lamellata. 7 



except in the Anomice, Ostrece and Pectinidce, in which, as the 

 foot is reduced almost to nothing, the mass of the body is the 

 only point d'appui ; but when the dome of the shell of the Pho- 

 ladidea papyracea is removed, the dark basal point of the stylet 

 presents itself in the centre of the mottled belly, precisely where 

 the foot is placed in the group of the Pholades, and in this case 

 it appears to act as a substitute. 



The siphonal apparatus consists of a long elastic sheath, 

 which is often protruded to double the length of the shell, but 

 in a state of half-extension it becomes highly corrugated ; it is 

 clothed with a dull red-brown epidermis, under which it is 

 bluish white ; the margin of its terminus is finely fringed with 

 short white cirrhi ; within the sheath are the anal and branchial 

 tubes, the former with the margin quite plain, but exserts a tu- 

 bular hyaline process ; the latter is encircled by about twenty 

 white cirrhi of different lengths. 



The liver is green, and situated as usual on the dorsal range. 

 There are on each side the body a pair of pale reddish brown 

 elongated suboval branchiae, the upper one being much the 

 smallest, which are finely striated on the outer surfaces ; their pos- 

 terior extremities suddenly become linear, and are then deposited 

 in the branchial tube ; there are also two long flat linear palpi on 

 each side, with lanceolate points ; these are more striated than 

 the branchiae. The body is centrally subglobose, but tapers pos- 

 teally and anteally to a blunt terminus, and the whole of it pre- 

 sents, especially in the genial season, a mottled mass of flaky 

 white subrotund spots or dots, with one of the termini of the 

 elastic appendage appearing in the centre of the anterior extre- 

 mity. With regard to the foot, as I have already observed, not 

 a trace is visible, having vanished for reasons to be spoken of in 

 another place. 



Pholadidea papyracea, Brit. Moll. 

 Pholas lamellata, auctorum. 



Animal nearly of the form we have just described; mantle 

 closed, except a large aperture for the passage of the foot, which 

 in this form of the P. papyracea is most apparent. The branchial 

 processes and siphonal tubes are, in the most minute points, 

 similar to those organs in the form styled Pholadidea papyracea 

 to which we refer ; the body, as in it, is subglobose, and pro- 

 duced posteally and anteally to an obtuse point, and it is gene- 

 rally of a bluish hyaline colour, with some fine anastomosing 

 lines throughout its surface, but has nothing of the mottled ap- 

 pearance of Pholadidea papyracea ; the shape of the branchiae is 

 the same as in its congener, but their striae are more delicate and 

 colour of the palest yellow ; these are the mere variations of ado- 

 lescence, and generally prevail where specific identity cannot be 



