Mr. S. P. Woodward on the Habits of Bivalve Shell-fish. 41 5 



only two tentacles, which, instead of being placed on the head, 

 as in Philomycus and all the other Arionidce and Helicidce, are 

 placed in the front part of the mantle. All these characters in- 

 duce me to regard it as the type of a new family of Fulmonata, 

 which may be called Janellidce. 



XL. — Notes on the Habits of Bivalve Shell-fish. 



By S. P. WOODWAKD. 



During the past summer I spent some time with Mr. Mackie 

 at Folkestone, and being obliged to remain within-doors the 

 greater part of each day, I collected a number of living Bivalves, 

 and kept them in pans of salt water, to watch them at my leisure. 

 The first species met with were Pholas dactylus and Candida, 

 whose colonies are frequent in the beach near low-water mark, 

 wherever a clear space occurs amongst the blocks of Kentish-rag 

 with which the shore is encumbered. The burrows of the Pho- 

 lades are in black sandy mud, from which they are easily dis- 

 lodged. At some spots the inhabitants have perished, but the 

 living colonies are readily discovered by treading heavily, or 

 striking the beach with a stick, whereupon the alarmed inmates 

 spirt water from their burrows. The holes of the full-grown 

 Pholas dactylus are distinguishable by their larger size, and the 

 strong jets they send up ; the original small orifices have been 

 removed by the wasting of the beach, and the present openings, 

 an inch in diameter, were once the middle of each burrow ; they 

 are rendered somewhat smaller by a layer of light-coloured mud, 

 which fills up the space between the shell-fish and the wall of 

 its abode. When the shell is partly exposed the Pholas still 

 holds strongly with its great foot, which cannot be withdrawn 

 into the shell, and resembles a piece of translucent ice. 



Placed in a pan of sea watei", the smaller Pholades (P. Candida) 

 immediately protrude their siphons, and explore the surrounding 

 bottom with them in a remarkably worm-like manner. The 

 young of P. dactylus only pushes itself about with its siphons. 

 The branchial currents commence instantly, and never cease 

 unless the creatures are disturbed. The force and volume of these 

 currents are quite marvellous to those who witness them for the 

 first time. The inhalant orifice is trumpet-shaped, and guarded 

 with cirri ; the exhalant is a little contracted, and in P. dactylus 

 projects beyond the other. The foot completely fills the pedal 

 orifice, allowing neither ingress nor egress to currents of water. 

 The current which sets into the branchial siphon carries with it 

 whatever floating particles the water contains, whilst the stream 

 which issues from the exhalant orifice is perfectly clear. How- 

 ever turbid the water may be, it is soon filtered, and the same thing 



