230 PLETJROBRANCHUS. 



PLANULARIA. Defr. Peneroplis, Montf. A genus of micro- 

 scopic Foraminifera. 



PLANULINA. D'Orb. A genus of microscopic Foraminifera. 



PLANULITES. Lam. Discorbites of the same author. A genus 

 of microscopic Foraminifera. 



PLATIRIS. Lea. (irXarvQ, platus, wide ; ipig, iris.) A genus 

 including several species of Nayades, referred to Iridina, Lam. 

 The genus Platiris is divided into two sub-genera. Iridina, species 

 which have crenulated margins ; I. Ovata, I. exotica, Spatha, Lea; 

 those with smooth or very slightly crenulated hinges, S. rubeus, 

 S. Solenoides, Mycetopus, D'Orb. Fig. 151. 



PLATYLEPAS. (ttXcitvq, platus, wide ; Xettuq, lepas, rock.) Order. 

 Sessile Cirripedes, Lam. Fam. Balanidea, Bl. — Descr. Conical, 

 depressed, consisting of six valves, each divided internally by an 

 angular plate jutting from the centre (like the buttress of a wall ) ; 

 operculum consisting of four valves in pairs. — Obs. This genus 

 differs from Balanus, Coronula, &c. in the internal structure of the 

 valves. De Blainville's description of Chthalamus partly agrees 

 with this. Fig. 19. 



PLECTOPHORUS. Fer. (TrXiy/crpoy, plectron, spur; (popeio, 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. 



PLETJROBRANCHUS. Cuv. (IlXevpa, pleura, the side ; Branchice, 

 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. 



