CATOPHRAGMUS IMBRICATUS. _G. B. Sowerby._ Genera of Recent and Fossil
Shells, Plate.
_Basis calcareous: caudal appendages present._
_Hab._--Antigua, West Indies, attached to a _Tetraclita porosa_.
As stated under the genus, this species is known from two specimens
in the British Museum, one of which is full-sized, being three
quarters of an inch in diameter, but is destitute of the outermost
whorls, of the basis, opercular valves, and animal's body; the other
is perfect, but very young, being barely two tenths of an inch in
basal diameter. As far as the characters can be made out from these
materials, I can perceive no difference from _C. polymerus_ in the
shell, excepting that in the small specimen of _C. imbricatus_, there
would appear to exist fewer whorls. The opercular valves are likewise
closely similar: in the scuta, however, of the young specimen in the
present species, the articular ridge seems to be a little broader,
but this is so variable a character that no confidence can be placed
in it: these valves, moreover, externally have a broad furrow along
the middle, running from the apex to the basal margin, which is not
the case with the scutum of _C. polymerus_; but then I have often
seen, in young specimens of Balanus, a similar furrow, which is quite
absent in full-grown specimens. When we come to the basis we find a
good diagnostic character, for here it is calcareous: it is rather
thin, solid, and white; towards the outside it is pitted with small
cavities, corresponding with the small teeth on the basal edges of
the compartments. The latter adhere firmly to the basis. The central
internal surface is covered by an irregular network of imbedded
cement-ducts, some of which bifurcate. From the description here
given, it will be seen that any figure would have been superfluous,
the last species having been so well illustrated.
_Mouth._--I can point out no difference, excepting that the palpi are
here more oval or less truncated at their ends; and that the lower
corner of the maxillæ seems to be more prominent. In the _Cirri_, the
rami of the first and second pairs are nearly equal in length: none
of the spines are coarsely pectinated. In the four posterior pairs
of cirri, instead of a tuft of small spines on each segment between
the pairs of main spines, there are only a few minute intermediate
spines: the dorsal tufts are also here smaller, but are, as in the
last species, composed of short thick, and longer thinner spines.
_Caudal Appendages._--This is the only species of sessile cirripede,
with the exception of the two species of Pachylasma, which possesses
these organs: they are situated on each side of the anus in the usual
position: they are minute, equalling in length only the lower segment
of the pedicel of the sixth cirrus: in a specimen in which the rami
of the sixth cirrus had eighteen or twenty segments, these appendages
consisted of only three tapering segments, supporting a few thick
spines.
_Branchiæ._--I believe I discovered these, consisting of two minute
pouches, placed at the carinal end of the sack: if this observation
be correct, this species differs from _C. polymerus_ in the much
smaller size of these organs.