124 PHOLADID. 
Famity PHOLADID A. 
Shell gaping at both ends; thin, white, brittle, and exceed- 
ingly 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 ; foot short and truncated; mantle closed 
in front, except the pedal orifice; siphons large, elongated, 
united nearly to their ends; orifices fringed; gills narrow, pro- 
longed into the exhalent siphon, attached throughout, closing 
the branchial chamber; palpi long. 
The cartilage of the hinge in these shells is small and internal ; 
the ligament is strong and elastic, situated externally, and both 
are further strengthened by an accessory membrane formed by 
the coriaceous end of the mantle, which issues between the 
anterior ends of the valves and covers the ligament; this exten- 
sion of the mantle is fixed by filaments which enter the dorsal 
cells and is furnished usually with calcareous plates which main- 
tain the valves in position. 
The Pholadidz perforate rocks, wood or clay; the burrows 
are vertical, quite symmetrical, and seldom in contact. 
SuBFAMILY PHOLADIN. 
Valves with an anterior gap which is never closed in the adult 
shells. 
Puotas, Linn., 1757. 
Etym.—Pholas, a burrowing shell-fish, from pholeo, to bore. 
Piddock. 
Syn.—Hypogeea and Hypogeoderma, Poli. 
Distr.—P. costata, Linn. (civ, 55-57). U.S. Fossil; Jur- 
assic, Cretaceous, Tertiary. 
Shell elongated, cylindrical; dorsal margin protected by two 
accessory valves; anterior and posterior in position; umbonal 
processes reflexed over the beaks, closely applied.  Pallial 
sinus reaching the centre of the shell. 
Animal with a large truncated foot, filling the pedal opening ; 
body with a fin-like termination ; combined siphons large, cylin- 
drical, with fringed orifices. P. costata is sold in the market of 
Havana, where it is an article of food. 
Mr. W. Woods remarks that on the coast of Normandy the 
Pholads are eaten in abundance, well seasoned and cooked with 
fine bread-crumbs and herbs. They are also reckoned a delicacy 
when pickled in vinegar. In the neighborhood of Dieppe a 
great many women and children, each provided with an iron 
