COXCHiFEKA. 503 



are formed by the siplional orifices wlien tKe animal continues 

 elongating, after having fixed its yalve and ceased to buiTow ; 

 or perhaps, in some instances, when it is compelled to lengthen 

 its tubes upwards by the accumulation of sediment. Brocchi 

 mentions that on breaking the tube of the fossil C. echinaia, he 

 sometimes found the shell of a Suxicava or Petricola beside the 

 loose valve of the Clavagella, into whose tube they must have 

 entered after its death. G. elongata is found in coral; C. 

 austrulis lives at low tide, and spirts out water when alarmed. 



Distribution, 6 species. Mediterranean, Australia, Pacific : — 

 11 fathoms. 



Fossil, 14 species. U. Greensand — . Britain, Sicily, 

 Southern India. 



AsPEEGiLLUM, Lam. Watering-pot shell. 



Type, A. vaginiferum, Pi. XXIII., Fig. 18. 



Synonym, 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 perforated 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 the mantle ; palpi lanceolate ; gills long, narrow, united 

 posteriorly, continued into and attached to the branchial siphon. 



Distribution, 21 species. Bed Sea, Java, Australia, New 

 Zealand ; in sand. 



Fossil, 1 species. (A ? Leognanum, Hoening. Miocene, Bor- 

 deaux. ) 



HUMPHREYIA, Gray. 

 Shell developed in the substance of the siphons, which grow 

 with the ventral side uppermost. 

 Distribution, 1 species. South Sea. 



Family XXI.— Pholadid^. 



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 im- 

 pression on the hinge-plate; pallial sinus veiy deep. 



Animal club-shaped, or worm-like ; foot short and tniiica.ted ; 



