39° 
MOLLUSCS. 
Choanopoma, Cistula, Tudora, Omphalotropis, are the principal forms of Cyclo- 
stomatidce. Some of the handsomest and largest species are found in Madagascar 
and Mauritius, hut some of the West Indian islands are noted for the immense 
number of species they produce. Among the Cyclophoridai, the most important 
groups are Cyclophoras, Leptopoma, Cyathoporrm, Pterocyclus, Opisthoporus 
Pupina, Cataulus, and Megalomastoma. The minute forms, known as Opistho- 
stoma are, perhaps, among the most wonderful structures of the whole family. 
The species comprised in the family Truncatellidce are all small, and live either 
between tide-marks ( Truncatella ) or upon the land ( Geomelania ). The shells are 
elongate, and in the young state terminate in a pointed spire, which is subse¬ 
quently cast off, the shells then assuming a truncate appearance at the top. They 
have a very peculiar mode of progression, resembling that of the looper cater¬ 
pillars, the end of the muzzle and the foot being successively advanced. The 
characteristic feature of the typical genus ( Pdipponyx ) of the allied family 
Pdipponyckidoe is the secretion by the foot of the animal of a shelly plate, which 
is attached by its outer surface to stones, shells, or other substances. It forms a 
permanent resting-place for the conical shell, and is attached to the adductor 
muscle of the animal. In some of the fossil species these lower plates are so greatly 
developed that they were at one time regarded as bivalved shells. Amalthea has 
a shell very like Hipponyx ; it does not form a basal plate, but excavates a hole 
in the surface of other shells to tit the aperture of its own. 
The members of the family Calyptrceidce are limpet-like in their mode of 
life, living attached to stones, shells, etc. The shells are more or less conical, but 
spiral towards the apex. The interior is either simple, as in Capidus, parted off 
by a transverse septum ( Crepidula ), or a cup-like process, varying in form, is 
developed in the upper part ( Crucibulum ). The animals have a short proboscis, 
two slender tentacles with the eyes near the base, and the mouth furnished with 
a radula bearing a prolonged tusk, like the Naticidae. Being permanently located, 
it becomes a matter of conjecture what they feed upon. Possibly the minute 
forms of life which abound in the sea form their staple nourishment. The various 
genera are for the most part recognisable by differences in the shell, the form 
of the internal septum and “ cup ” furnishing good characters. The number of 
living forms is considerable, and they are found in all seas. Two occur on the 
British coast,— Calyptrcea chinensis and Capidus liungaricus, —and a third, 
Crepidula fornicata, supposed to have been imported with American oysters, is 
becoming an established resident on the Essex coast. Closely allied to Capidus 
is Thyca crystallina, which lives parasitic upon star-fish at Mauritius and in 
other parts of the Indian Ocean. In the family Xenoplioridae are contained a 
remarkable group of molluscs known as carrier-shells, so-called from the instinctive 
habit some of them possess of carrying about with them shells, stones, and other 
substances, which they cement to the exterior of their own trochiform shells. 
Doubtless this concealment is to some extent protective. The animals bear some 
resemblance to Strombus, but their eyes are very inferior, and placed at the base 
of the tentacles. They are furnished with opercula, which, however, are more 
like those of Purpura than Strombus. They resemble the latter in their leaping 
and scrambling mode of progression, not gliding along on the sole of the foot 
