34
ANATlxVID^.
continually exercised by the strong and elastic cartilage
exceeds that of the shell ; and the latter being the weaker
body, gives way and is split in the conflict. Only one
species [T. distorta), which is comparatively more solid
than the others, resists the strain and remains uninjured.
The synonymy of the European species has been
lamentably perplexed ever since the time of Pennant,
notwithstanding the pains taken by Loven and the
authors of the ' British Mollusca^ to unravel the tangled
skein.
This makes it extremely difficult to define with
any certainty the geographical distribution of some of
these species.
Geologically Thracia appears to be an
ancient genus.
" Fossils of this form are found in the
lower Oolites, and doubtfully so in the Carboniferous
series" (S. Wood). It is the genus Odoncincta of Da
Costa, and has received other equally barbarous names
from modern authors. Cochlodesma, Couthouy, does
not difter in any respect except in the absence of an
ossicle : all the British species of Thracia possess this
appendage.
A. Nearly equilateral.
1. Thracia PRiETE^NUis^^ Pulteney.
Mya pratenuis, Pult. Cat. Dors. p. 28, pi. iv. f. 7. Cochlodesma prmtenue,
"r. & H. i. p. 235, pi. XV. f. 4.
Body thin, clear white : gills strongly pectinated, eacli
divided by an oblique furrow into two parts, the upper being
less deep than the lower portion : foot white.
Shell triangularly oval, compressed, opaque, somewhat
glossy ; right valve more convex than the left, and slightly
overlapping it: sculpture (besides the usual marks of growth),
close-set and microscopical transverse hair-like lines or scratches
* Very tliin.
ANATlxVID^.
continually exercised by the strong and elastic cartilage
exceeds that of the shell ; and the latter being the weaker
body, gives way and is split in the conflict. Only one
species [T. distorta), which is comparatively more solid
than the others, resists the strain and remains uninjured.
The synonymy of the European species has been
lamentably perplexed ever since the time of Pennant,
notwithstanding the pains taken by Loven and the
authors of the ' British Mollusca^ to unravel the tangled
skein.
This makes it extremely difficult to define with
any certainty the geographical distribution of some of
these species.
Geologically Thracia appears to be an
ancient genus.
" Fossils of this form are found in the
lower Oolites, and doubtfully so in the Carboniferous
series" (S. Wood). It is the genus Odoncincta of Da
Costa, and has received other equally barbarous names
from modern authors. Cochlodesma, Couthouy, does
not difter in any respect except in the absence of an
ossicle : all the British species of Thracia possess this
appendage.
A. Nearly equilateral.
1. Thracia PRiETE^NUis^^ Pulteney.
Mya pratenuis, Pult. Cat. Dors. p. 28, pi. iv. f. 7. Cochlodesma prmtenue,
"r. & H. i. p. 235, pi. XV. f. 4.
Body thin, clear white : gills strongly pectinated, eacli
divided by an oblique furrow into two parts, the upper being
less deep than the lower portion : foot white.
Shell triangularly oval, compressed, opaque, somewhat
glossy ; right valve more convex than the left, and slightly
overlapping it: sculpture (besides the usual marks of growth),
close-set and microscopical transverse hair-like lines or scratches
* Very tliin.