346 Div. 2. MOLLUSCA.— GASTEROPODES. Class 3, 



in the form of the respiratory organs, and, like thenij live in the sea; but they are hermaphro- 

 dites, like the Nudibranchiata and Pulmonea. 



The Pleurobranchus, Cuv.* 

 The cloak and the foot both jut beyond the body, which thus appears as if it were between two 

 hucklers. 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 branchiaj 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 tlie branchiffi. There are four 

 stomachs, of which the second is fleshy, sometimes armed with osseous pieces, and the third is garnislied 

 with prominent longitudinal laminae. The intestine is short. 



Tliere 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 {Pleurohranchidium, Blainv.), — 

 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. Tliere is no 

 trace of a shell. 

 The only known species is from the Mediterranean. 



The Aplv'sia, Lin. 



The margins of the foot are turned up into flexile crests, and, siUTOunding the back on every side, 

 they can be reflected over it. The head, supported on a neck of greater or less length, has the two 

 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 branchiai in the 

 form of complicated leaflets, attached to a broad membranous pedicle, and concealed by a little cloak, 

 equally membranous, which contains a horny flat shell. The anus is behind the branchiae, and is often 

 concealed under the lateral crests : the vulva is to the right in front, and the penis issues from under 

 the right tentaculum. A groove, which extends from the vulva to the very e.Ktremity of the penis, 

 conducts the semen thither in copulation. A membranous crop, of eucTuous 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 ccecum. The intestine is voluminous. 

 These animals feed on sea-weed. A peculiar gland pours out, througli an orifice near the vulva, a 

 hmpid humour, which is said to be very acrid in some species ; and from the edges of the .cloak there 

 oozes in abundance a deoii purple liquid, with which the animal discolours the wfiter of the sea when it 

 perceives danger to be at hand. Their ova aic laid in long glairy entangled filaments, as slender as 

 threads. 



There are found in our seas Apl. fasciata, Poiret, punctata, Cuv., and depilans, Linn. ; and the shores of foreign 

 countries possess several others. 



The Dolabella, Lam. — 

 Differs only from Aplysia in the position of the branchiae at the posterior extremity of the body, wliich 

 resembles a truncated cone. The lateral crest fits close to the branchial apparatus, leaNing merely a 

 narrow groove. Tlie shell is calcareous. 

 The species arc 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 

 water to the branchiaj. These have no cloak to cover them, but in other respects they resemble the 

 branchiae of tlie Aplysia ; and the organization of the two genera is otherwise similar. In 



• The same as the Liimrlttiria of Montajrn. [a name which thi- Btitanists have usurped,] and the BerthcUa of Blamvillc. [This ^enuB, Plctt* 

 robranchtca. Umbrella, Spiricellai.'wid Siphoiiia, arc placed in tlic preceding order by Kini;.J 



