CONCIIIFEUA. 327 



AsPERGiLLUM, Lam. Wateriug-pot shell. 



Type, A. vaginiferum, PI. XXIII. fig. 18. Syn. Clepsydra, Schum. 



Shell small, equilateral, cemented to the lower end of a shelly tube, the 

 umbones alone visible externally ; tube elongated, closed below by a perfo- 

 rated disk with a minute central fissure ; siphonal end plain or ornamented 

 with (1—8) ruffles. 



Animal elongated ; mantle closed, thickened and fringed with filaments 

 in front ; foot conical, anterior, opposed to a minute slit in tlie mantle ; 

 palpi lanceolate ; gills long, narrow, united posteriorly, continued into and 

 attached to the branchial siphon. 



Disir. 4 sp. Red Sea, Java, Australia, N. Zealand ; in sand. 



Fossil, 1 sp. (A ? Leognanum, Haning. Miocene, Bordeaux.) 



FAMILY XXI. PHOLADID.E. 



Shell gaping at both ends ; thin, white, brittle and exceedingly hard ; 

 armed in front with rasp-like imbrications ; without hinge or ligament, but 

 often strengthened externally by accessory valves ; hinge-plate reflected over 

 the umbones, and a long curved muscular process beneath each ; anterior 

 muscular impression on the hinge-plate; pallial sinus very deep. 



Animal club-shaped, or Avorm-like; foot short and truncated; mantle 

 closed in front, except the pedal orifice; siphons large, elongated, united 

 nearly to their ends ; orifices fringed ; gills narrow^ prolonged into the ex- 

 halent siphon, attached throughout, closing the branchial chamber: palpi 

 long ; anterior shell-muscle acting as substitute for a ligament. 



The Pholadidcp perforate all substances that are softer than their own 

 valves (p. 242);* the burrows of Pholas are vertical, quite symmetrical, and 

 seldom in contact. The ship-worms {Teredines) also make symmetrical per- 

 forations, and however tortuous and crowded never invade each other, guided 

 either by the sense of hearing or by the yielding of the wood. The burrow 



* M. CaiUiaud has proved that these valves are quite equal to the work of boring 

 in limestone, by imitating the natural conditions as nearly as possible, and 7?2fl/a'H<;r 

 such a hole with them. Mr. Robertson also, has kept the living Pholades in blocks of 

 chalk, by the sea-side at Brighton, and has watched the progress of the work. They 

 turn from side to side never going more than half-round in their burrow, and cease to 

 work as soon as the hole is deep enough to shelter them; the chalk powder is ejected 

 at intervals by spasmodic contractions from the branchial siphon, the space between 

 the shell and burrow being filled with this mud. (Journ. Conch. 18.53, p. 31 J. j It is 

 to be remarked that the condition of the Pholades is alwaj's related to the nature of 

 the material in which they are found burrowing; in soft sea beds they attain the 

 largest size and greatest perfection, whilst in hard, and especially gritty rock, they 

 are dwarfed in size and all prominent points and ridges appear worn by friction. Ko 

 notice has been taken of the hypothesis Avhich ascribes the perforation of rocks, &c., 

 to ciliary action, because, in fact, there is no current between the shell or siphons and 

 the wall of the tube. 



