MOLLUSCA. 
354 
in the form of the respiratory organs, and, like them, live in the sea ; hut they are hermaphro- 
dites, like the Nudibranchiata and Pulmonea. 
The Pleurobranchus, Cut.* 
The cloak and the foot both jut beyond the body, which thus appears as if it were between two 
bucklers. The former contains, in some species, a little oval calcareous plate ; in others, a horny one, 
and in either case it is situated above the head. The branchiae are placed along the right side, in a 
groove between the cloak and foot, and represent a series of pyramids divided into triangular leaflets. 
The mouth, in the form of a small proboscis, is overhung with an emarginate lip, and with two tubular 
cleft tentacula ; the orifices of generation are before, and the anus behind the branchiae. There are four 
stomachs, of which the second is fleshy, sometimes armed with osseous pieces, and the third is garnished 
with prominent longitudinal laminae. The intestine is short. 
There are different species in the Mediterranean and Indian Ocean, some of which are large and beautiful. [We 
have two British species.] 
The Pleurobranch^a, Meckel {Pleurobranchidium, Blainv.), — i 
Has the branchiae and the orifices of generation situated as in Pleurobranchus ; but the anus is above 
the branchiae ; the margins of the cloak and of the foot project but a little, and upon the front of the ' 
cloak are four short distant tentacula, forming a square which forces a comparison with the anterior 
disk of the Aceres. I find but one stomach, with thin parietes, which is a mere dilatation of the 
intestine. A greatly divided glandular organ opens outwardly behind the genital orifices. There is no 
trace of a shell. 
The only known species is from the Mediterranean. 
The Aplvsia, Lin. ’ 
The margins of the foot are turned up into flexile crests, and, surrounding the back on every side, |i 
they can be reflected over it. The head, supported on a neck of greater or less length, has the two II 
superior tentacula hollowed like the ears of a quadruped, and two others of a flattened shape at the end ^ 
of the inferior lip ; the eyes at the base of the former. Upon the back we find the branchiae in the '! 
form of complicated leaflets, attached to a broad membranous pedicle, and concealed by a little cloak, |j 
equally membranous, which contains a horny flat shell. The anus is behind the branchiae, and is often li 
concealed under the lateral crests : the vulva is to the right in front, and the penis issues from under ,jl 
the right tentaculum. A groove, whieh extends from the vulva to the very extremity of the penis, 
conducts the semen thither in copulation. A membranous crop, of enormous size, leads into a muscular 
gizzard, armed inside with many cartilaginous and pyramidal bodies ; and this is followed by a third 
stomach beset with sharp hooks, and a fourth in the form of a coecum. The intestine is voluminous. ' 
These animals feed on sea-weed. A peculiar gland pours out, through an orifice near the vulva, a 
limpid humour, which is said to be very acrid in some species ; and from the edges of the cloak there 
oozes in abundance a deep purple liquid, with which the animal discolours the water of the sea when it j| 
perceives danger to be at hand. Their ova are laid in long glairy entangled filaments, as slender as j 
threads. I) 
There are found in our seas Apl. fasciata, Poiret, punctata, Cuv., and depilans, Linn. ; and the shores of foreign | 
countries possess several others. || j 
The Dolabella, Lam. — 
Differs only from Aplysia in the position of the branchite at the posterior extremity of the body, which ,|l 
resembles a truncated cone. The lateral crest fits close to the branchial apparatus, leaving merely a ‘j 
narrow groove. The shell is calcareous. !' 
The species are found in the Mediterranean and in the Indian Ocean. | 
The Notarchus, Cuv. — 
Has the lateral crests united and covering the back, leaving merely a longitudinal fissure to conduct n 
water to the branchiae. These have no cloak to cover them, but in other respects they resemble the | 
branchiae of the Aplysia ; and the organization of the two genera is otherwise similar. In -|| 
* The same as the Liwiellaria of Montagu, [a name which the Botanists have usurped,] and the Berthella of Blainville. [This genus, Pleu- 
robranchaia. Umbrella, Spiricella,and Siphonia, are placed in the preceding order by Rang.] 
