ORDER NUDIBRANCHIATA. 37 
Doris, Cuv. 
The anus opens on the posterior part of the back, the gills 
being arranged in a circle round it, under the form of little 
arbuscule, the whole resembling a sort of flower; the mouth 
is a small proboscis, situated under the anterior margin of the 
mantle, and furnished with two little conical tentacule. Two 
other claviform tentacula arise from the anterior and superior 
part of the mantle. The openings of the genital organs are 
approximated under its right margin; the stomach is membra- 
nous; a gland, interlaced with the liver, excretes a peculiar 
fluid through a hole near the anus. The species are nume- 
rous, and some of them large. ‘They are found in every sea, 
where their eggs, like gelatinous bands, are diffused over 
stones, sea-weed, &c. 
Species with an oval mantle projecting beyond the foot, 
Doris verrucosa, L.; Doris argo, L.; Doris obvelata, &c. 
Prismatic species, where the mantle is almost as narrow as 
the foot, Doris lacera, Cuv.; D. atromarginata, Id., &c. 
ONCHIDORA, Blainv., 
Only differs from doris in the separation of the genital organs, 
the orifices of which communicate by a furrow running along 
the right side, as in onchidium. (Onchidora Leachii, Blainv.) 
PLOCAMEROS, Leuckard, 
Have all the characters of the onchidore, in addition to which 
the anterior margin of their mantle is ornamented with nume- 
rous branched tentacula. (Plocameros ocellatus, Leach.) 
POLYCERA, Cww. 
The gills, as in doris, on the hind part of the body, but 
more simple, and followed by two membranaceous lamine, 
which cover them in moments of danger. Anterior to the 
