GINGLYMACONCHA. PHOLADIDZ. 249 
FAMILY I. PHOLADID. 
Pholas, Auctorum. 
Hypogeea, Poli. 
Shell elongate, equivalve or slightly imequivalve, generally 
gaping anteriorly, but rarely behind; internally, under the 
umbones, bearing a shelly process or apophysis. Umbones 
anterior, generally concealed by the reflection of the shell. 
Cardinal ligament minute or wanting. Hinge without teeth. 
Epidermis thin, covering the respiratory tubes, which are very 
long, jomed together, equally long, with their extremities ob- 
tuse. Mantle everywhere united, excepting at the exit of the 
foot. Foot very short, ovately depressed, marked with an im- 
pression at its extremity, as if it had been stabbed. Lip with 
very long, slender and acuminate lobes. Branchiz very long 
and slender, produced to the middle of the lower tube. Abdo- 
men acuminate behind. Anterior adductor muscle attached to 
the reflected part of the shell, and consequently performing the 
function of opening the valves. 
All the animals of this family habit the sea; perforating 
rocks, shells or wood. 
The principal characters of this Family consist in the reflec- 
tion of the shell over or before the umbones; the consequent 
extraordinary change in the function of the anterior abductor 
muscle, which supplies the office of the cardinal ligament, 
which is either wanting or very diminutive in size; the pre- 
sence of a process or apophysis, in each valve, arising from the 
hollow of the umbones ; and lastly the supplementary pieces of 
shell, which protect the anterior abductor muscle, or serve to 
give greater strength to the dorsal portions of the epidermis. 
These supplementary shells I have named from their actual 
position, wmbonic, when they cover the umbones; post-wm- 
bonic, when situated behind the umbones ; dorsal, when cover- 
ing the dorsal aspect ; and ventral, when protecting the inferior 
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