PLECTOPHORUS. Fer. ([Greek: plêktron], _plectron_, spur; [Greek: phoreô], _phoreo_, to carry.) A genus consisting of small testaceous appendages fixed on the posterior extremity of a species of slug. P. corninus, fig. 260. PLEIODON. Conrad. IRIDINA, Lam. _Fam._ Nayades, Lam. PLEKOCHEILUS. Guild. AURICULA Caprella, Lam. CARYCHIUM undulatum, Leach. (CAPRELLA, Nonnull.) This proposed genus is described as scarcely umbilical, dextral, oval, spiral; with the spire elevated, obtuse; the two last whorls very large, ventricose; aperture entire, elongated; columella with a single plait; the plait concave, inflected. Fig. 522, 523. PLEUROBRANCHUS. Cuv. ([Greek: Pleura], _pleura_, the side; _Branchiæ_, gills.) _Fam._ Semiphyllidiana, Lam. Subaplysiacea, Bl.--_Descr._ Internal, thin, haliotoid, slightly convex towards the spiral apex; aperture entire.--_Obs._ This is a very light shell, delicately coloured, resembling Aplysia, but differing in the integrity of the margin. Fig. 232, P. membranaceus. PLEUROCERUS. Rafinesque. A genus very imperfectly described in the "Journal de Physique" as "oval, or pyramidal; aperture oblong; outer lip thin; inner lip truncated at the columella, which is smooth and tortuous, not umbilicated. Operculum horny or membranaceous." De Blainville, in giving this description, remarks that he has neither seen the animal nor the shell of this genus, which he imagines to have been formed from the "Paludine Coupée de M. Say." PLEURORYNCHUS. Phillips. ([Greek: Pleura], _pleura_, the side; [Greek: runchos], _rynchus_, a beak.) A genus founded upon a very singular species of CARDIUM, distinguished by the short anterior side, and the elongation of the hinge line into auricular processes, which are truncated at the extremities. C. Hibernicum from the Black Rock near Dublin, which is vulgarly called Asses-hoof, and C. elongatum (Sow. Min. Con. vol. I. 82.), form part of this genus.