THRACIA.
41
It is the T. declivis of jMacgillivray^ T. ventncosa of
Philippic and (apparently) the T. Scheepmakeri of
Dunker.
B. Posterior side usually larger.
5. T. DisTOR TA^, Montagu.
Mya dhtorfa, Mont. Test. Brit. p. 42, t. i. f. 1. T. distorta, F. & H. i.
p. 231, pi. xvii. f. 1, 2, 3, 8, and (animal) pi. H. f. 5.
Body roundish- oval, white : tubes rather short, and somewhat more united towards their bases than in the other British
Tliracice ; the branchial or lower tube is often extended more
than half an inch, while the other remains quiescent ; previously to the former being withcbawn, it is always globularly
inflated at its extremity, which inflation increases until it extends near the margin of the shell, and the tube then suddenly
collapses ; during the inflation the terminal cirri disappear,
and they only become visible when the tube is at rest : gills
large and brown : palps nearly equal and pectinated : foot
short and linguiform.
Shell varying in shape from round to oval, more or less
distorted and often sinuous, generally convex but sometimes
flattened, more solid in proportion to its size than the other
species, opaque and lustreless : sculpture, minute and crowded
tubercles or granulations of equal size, arranged^ in concentric
although irregular rows; marks of growth distinct: colour
milk-white, with occasionally a yellowish tinge: epidermis
membranous, abraded in front and only to be seen at the
edges, dingy brown : margins rounded on the anterior side
and in front, somewhat truncated or wedge-shaped on the
posterior side, which is in most instances (but not invariably)
larger or more elongated than the other side, and obscurely
angulated ; dorsal margins obtuse-angled : heahs sharp and
entire, slightly inchned to the posterior side ; umbones rather prominent : ligament short, of various shades of colour
from yellowish to dark brown, separating the valves by an
oval gap : cartilage strong, yellowish -brown or horncolour,
contained in a thick triangular receptacle, which is set obliquely and projects considerably within each valve ; fulcral
* Distorted.
41
It is the T. declivis of jMacgillivray^ T. ventncosa of
Philippic and (apparently) the T. Scheepmakeri of
Dunker.
B. Posterior side usually larger.
5. T. DisTOR TA^, Montagu.
Mya dhtorfa, Mont. Test. Brit. p. 42, t. i. f. 1. T. distorta, F. & H. i.
p. 231, pi. xvii. f. 1, 2, 3, 8, and (animal) pi. H. f. 5.
Body roundish- oval, white : tubes rather short, and somewhat more united towards their bases than in the other British
Tliracice ; the branchial or lower tube is often extended more
than half an inch, while the other remains quiescent ; previously to the former being withcbawn, it is always globularly
inflated at its extremity, which inflation increases until it extends near the margin of the shell, and the tube then suddenly
collapses ; during the inflation the terminal cirri disappear,
and they only become visible when the tube is at rest : gills
large and brown : palps nearly equal and pectinated : foot
short and linguiform.
Shell varying in shape from round to oval, more or less
distorted and often sinuous, generally convex but sometimes
flattened, more solid in proportion to its size than the other
species, opaque and lustreless : sculpture, minute and crowded
tubercles or granulations of equal size, arranged^ in concentric
although irregular rows; marks of growth distinct: colour
milk-white, with occasionally a yellowish tinge: epidermis
membranous, abraded in front and only to be seen at the
edges, dingy brown : margins rounded on the anterior side
and in front, somewhat truncated or wedge-shaped on the
posterior side, which is in most instances (but not invariably)
larger or more elongated than the other side, and obscurely
angulated ; dorsal margins obtuse-angled : heahs sharp and
entire, slightly inchned to the posterior side ; umbones rather prominent : ligament short, of various shades of colour
from yellowish to dark brown, separating the valves by an
oval gap : cartilage strong, yellowish -brown or horncolour,
contained in a thick triangular receptacle, which is set obliquely and projects considerably within each valve ; fulcral
* Distorted.