GASTEROPODA TECTIBRANCHIATA. 345 



more or less covered by the mantle, in which a small shell is 

 generally contained. They approach the Pectinibranchiata in 

 the form of the organs of respiration, and like them inhabit 

 the Ocean ; but they are all hermaphrodites like the Nudi- 

 branchiata and the Pulnionea. 



Pleurobranchus, Cuv. 



The body equally overlapped by the mantle and by the foot, as if it 

 were between two shields. In some species a little oval calcareous 

 lamina is contained in the mantle, and a horny one in that of others; 

 the mantle is emarginated above the head. The branchiae are attach- 

 ed along the right side in the furrow, between the mantle and the 

 jfe* foot, forming a series of pyramids divided into triangular laminulae. 

 The mouth, a small proboscis, is surmounted by an emarginated lip 

 and by two tubular and cleft tentacula; the genital orifices are be- 

 fore, and the anus behind the branchix. There are four stomachs, 

 the second of which is fleshy and sometimes armed with bony ap- 

 pendages, and the third, furnished internally with salient longitudi- 

 nal 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(l). 



Pleurobranch^a, Meckel. Pleurobranchidium, B1. 



The branchiae and genital orifices situated as in Pleurobranchus; 

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

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

 short, distant tentacula, forming a square that 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. 



(1) Pleurohranchus Peronii, Cuv., Ann. du Mus., V, xviii, 1, 2; PI. iubercu- 

 latus, Meckel., Anat. Compar., I, v, 33 40; and some new species, such 

 as the Pleur. oblongus, Descr. de I'Eg-., Moll. Gaster., pi. iii, f. 1; PI. aurantiacus. 

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

 Forsk., pi. xxviii, and Leuckai-d, App., lluppel., An. Invert., pi. v; PI. citrinus, 

 lb., f. 1. 



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

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

 vation applies to the Berthelia 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 Pleurohranchus. The PI. oblongus would belong to 

 it, and even the PI. luniceps. 

 Vol. II. 2 T 



-'m 



