MOLLUSCA+ 161 
abdominal cavity, and which consists of a vessel forming a 
great number of complicated convolutions, liberally suppli- 
ed with bloodvessels. The duct proceeds from this mass, 
undergoes for a short space a sudden thickening of its walls, 
after which it again contracts, and, before it terminates in a 
perforated glandular knob in the recess, it contains a pe- 
dunculated fleshy body, with a sharp-pointed corneous ex- 
tremity, prohably capable of being protruded into the recess 
and cavity. The parts which are considered as forming the 
female organs, or those which are connected with the sexu- 
al cavity on the right side of the anus, consist of an ovari- 
um, divided into two lobes, each of which may be perceived 
to be again minutely subdivided. The oviduct is tortuous, 
and passes through a glandular body, which, in the other 
gasteropoda, is regarded as the testicle. The pedunculated 
vesicle gives out two ducts, one of which goes to the testi- 
cle, the other to the uterus. It is difficult to form even a 
conjecture regarding the uses of all this complicated sexual 
apparatus. The subject can only be elucidated by an at- 
tentive examination of the condition of the organs at differ- 
ent seasons of the year, and by studying, at the same time, 
the habits of the animals. 
The preceding description of the characters of the genus 
is taken from the anatomical details of a species found 
creeping upon the rocks under water in the Mauritius, by 
M. Peron, which Cuvier referred to the genus Onchidium 
of Buchanan, already noticed. We have ventured to insti- 
tute the genus, and to name it in honour of the discoverer 
of the first ascertained species. Cuvier conjectures that it 
breathes free air, and has accordingly inserted it among the 
pulmones aquatique. Some doubts, however, may reason- 
ably be entertained as to the truth of this supposition. It 
