GASTEROPODA TECTIBRANCHIATA. 45 



are attached along the right side in the furrow, between the mantle 

 and the foot, forming a series of pyramids divided into triangular 

 laminulae. The mouth in the form of a small proboscis, is sur- 

 mounted by an emarginated lip, and by two tubular and cleft 

 tentacula ; the genital orifices are before, and the anus behind the 

 branchiae. There are four stomachs, the second of which is fleshy 

 and sometimes armed with bony appendages, and the third, furnished 

 internally with salient longitudinal laminae ; the intestine is short. 



Various species inhabit both the Mediterranean and the At- 

 lantic, some of which are large and marked with the most 

 beautiful colours*. 



PLEUROBRANCMA, Meckel. PLEUROBRANCHIDIUM, Bl. 



Have the branchiae and genital orifices situated as in Pleurobranchus ; 

 but the anus is above the branchiae, the margins of the mantle and 

 foot project but little, and on the fore-part of the former are four 

 short, distant tentacula, forming a square, which reminds the observer 

 of the anterior disk of the Acerae. I can find but one stomach, which 

 is merely a dilatation of the canal, with thin parietes. A multifidous 

 glandular organ opens behind the genital orifices ; there is no vestige 

 of a shell. 



Pleurob. Meckelii, Leve, Diss. de Pleur., 1813f. The only 

 species known ; from the Mediterranean. 



APLYSIA, Lin.\. 



Have the margins of the foot turned up into flexible crests, sur- 

 rounding the back in all its parts, and even susceptible of being 

 reflected over it ; the head supported by a neck more or less long ; 

 .two superior tentacula excavated like the ears of a quadruped, with 

 two flattened ones on the edge of the lower lip ; the eyes above the 

 former. The branchiae are on the back, and consists of highly com- 

 plicated leaflets attached to a broad membranous pedicle, covered by 

 a small mantle also membranous, in the thickness of which is a flat 



Pleurobranchus Peronii, Cuv., Ann. du Mus., V, xviii 1,2; PI. tubercu- 

 latus, Meckel., Anat. Compar., 1, v, 3340; and some new species, such as 

 the Pleur. oblongus, Descr. de 1'Eg., Moll. Caster., pi. iii, f. 1 ; Plaur auranliacus, 

 Id., Risso., Hist. Nat. Merid. IV, pi. i, f. 8 ; PI. luniceps, Cuv. ; PI. Fonkalii, 

 Forsk., pi. x xviii, and Leuckard, App., Ruppel., An. Invert., pi. v; PI. citrinus, 

 Ib., f. 1. 



The genus LAMELLARIA, Montag., Lin. Trans., XI, pi. xii, f. 3 and 4, does not 

 appear to me to differ in any essential point from Pleurobranchus ; the same obser- 

 vation applies to the BKRTHBLLA of Blainv., Malac., pi. xliii, f. 1. The latter is 

 distinguished merely because the mantle is not emarginated above the head, as is 

 the case in many species of Pleurobranchus. The PI. oblongus would belong to it, 

 and even the PI. luniceps. 



t It is the genus Plturobranchidium of Blainv., Malac., pi. xliii, f. 3 ; but not as 

 he thinks the Pltvrobranchus tuberculatus of Meckel. 



t Aphuia, which cannot clean itself, a name given by Aristotle to certain 

 Zoophytes. Linnaeus erroneously applied it as above. The animals here spoken of 

 were well known to the ancients, who styled them Sea-Hares, and attributed to 

 them many fabulous properties. 



