PHOLAS. 171 



with an exsertile tubular hyaline process ; the latter is encir- 

 cled 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 of 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 

 posterior 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 sub- 

 globose, but tapers posteally and anteally to a blunt terminus, 

 and the whole of it presents, 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 extremity. With regard to the foot, as I have 

 already observed, not a trace is visible, having vanished for 

 reasons to be spoken of below. 



P. PAPYRACEA, JUV., 



Pholadidea papyracea, Brit. Moll. i. p. 123, pi. 5. f. 3, 4, 5, 6 ; pi. 2. 



f. 1 ; (animal) pi. E. f. 4. 

 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 produced posteally and anteally to an obtuse 

 point, and it is generally of a bluish-hyaline colour, with some 

 fine anastomosing lines throughout its surface, but has nothing 

 of the mottled appearance 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 adolescence, and generally prevail where 

 specific identity cannot be doubted, and they are deposited 

 partially as in its congener, in the branchial tube : the palpi 

 and liver exhibit no variation. 



