POROMYA.
45
The structure of the shell is very remarkable, althoug^h
not differing much from that of T/iracia. The external
layer consists of crowded oblong cells having their ends
outward, and the inner layer is nacreous ; the cellular
part is easily rubbed off. The mantle is said to be open
in front, an unusual character in this group. Further
])articulars of the animal are desirable.
This genus is the Embla of Loven, and (according to
Chenu) the Eucharis of Eecluz.
PoROMYA granula'ta*, Nyst and Westendorp.
Corbula granulato, Nyst & West. Coq. Foss. d'Anvers, p. 6, pi. 3. f. 3. P.
granulata, F. & H. i. p. 204, pi. ix. f. 4-G, and (animal) pi. W. f. 2.
Body crcamcolour : mantle open in front : tubes encircled at
their bases by a fringe of 18 or 20 tentacular filaments, which
expand like the petals of a flower, and are sometimes folded
back on the posterior side of the shell : foot very transparent.
Shell somewhat quadrangular or rhomboidal (the right
valve larger than the left and slightly overlapping it), moderately convex, fragile ; externally it is opaque and of a dark
hue, but when the superficial or granular coating is removed,
it is semitransparent and glossy : scidptiire, very minute and
close-set tubercles of nearly equal size, arranged in longitudinal rows, and occasional but slight marks of growth : colour
dusky outside, and whitish imder the surface-layer : epidermis
dark brown, visible only at the edges, and especially at the
back (where it forms a kind of elongated ligament on both
sides of the beak) : margins rounded on the anterior side,
shghtly curved in front, indented near the posterior side, which
is obliquely truncated and has a distinct ridge extending from
the beak to the posterior angle, with a broad fold on either
side of it ; posterior dorsal margin longer and straighter than
the other : heahs blunt and calyciform ; umbones prominent
cartilage yellowish -brown, set rather obliquely in an obtuselj^
angular receptacle, which does not project far within : hingeline gradually curved : hinge-plate thickened on both sides of
the beak : teeth, in the right valve an erect, blunt and tuber* Gninulated.
45
The structure of the shell is very remarkable, althoug^h
not differing much from that of T/iracia. The external
layer consists of crowded oblong cells having their ends
outward, and the inner layer is nacreous ; the cellular
part is easily rubbed off. The mantle is said to be open
in front, an unusual character in this group. Further
])articulars of the animal are desirable.
This genus is the Embla of Loven, and (according to
Chenu) the Eucharis of Eecluz.
PoROMYA granula'ta*, Nyst and Westendorp.
Corbula granulato, Nyst & West. Coq. Foss. d'Anvers, p. 6, pi. 3. f. 3. P.
granulata, F. & H. i. p. 204, pi. ix. f. 4-G, and (animal) pi. W. f. 2.
Body crcamcolour : mantle open in front : tubes encircled at
their bases by a fringe of 18 or 20 tentacular filaments, which
expand like the petals of a flower, and are sometimes folded
back on the posterior side of the shell : foot very transparent.
Shell somewhat quadrangular or rhomboidal (the right
valve larger than the left and slightly overlapping it), moderately convex, fragile ; externally it is opaque and of a dark
hue, but when the superficial or granular coating is removed,
it is semitransparent and glossy : scidptiire, very minute and
close-set tubercles of nearly equal size, arranged in longitudinal rows, and occasional but slight marks of growth : colour
dusky outside, and whitish imder the surface-layer : epidermis
dark brown, visible only at the edges, and especially at the
back (where it forms a kind of elongated ligament on both
sides of the beak) : margins rounded on the anterior side,
shghtly curved in front, indented near the posterior side, which
is obliquely truncated and has a distinct ridge extending from
the beak to the posterior angle, with a broad fold on either
side of it ; posterior dorsal margin longer and straighter than
the other : heahs blunt and calyciform ; umbones prominent
cartilage yellowish -brown, set rather obliquely in an obtuselj^
angular receptacle, which does not project far within : hingeline gradually curved : hinge-plate thickened on both sides of
the beak : teeth, in the right valve an erect, blunt and tuber* Gninulated.