246 PLETJEOBRANCHUS. 



PLANULAEIA. Defr. Peneeoplis, Montf. A genus of mi- 

 croscopic Foraminifera. 

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

 PLANULITES. Lam. Discoebites of the same author. A 



genus of microscopic Poraminifera. 

 PLATIEIS. Lea. {irXarvg, platus, wide ; tptg, iris.} A genus 

 including several species of ]N"ayadeSj referred to Ieidina, 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. Pig. 151. 

 PLATYLEPAS. (TrXarve, platus, wide ; \e7rac, lepas, rock.) 

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

 Conical, depressed, consisting of six valves, each divided inter- 

 nally by an angular plate jutting from the centre (like the 

 buttress of a wall) ; operculum consisting of fotu* valves in 

 pairs. — Obs. This genus differs from Balanus, Coronula, &c. in 

 the internal structure of the valves. De BlainviUe's descrip- 

 tion of Chthalamus partly agrees with this. PL i. fig. 19. 

 PLAXIPHOEA. Gray. Chiton Carmichselis, &c. 

 PLECTOPHOEUS, (Per. 7rX^K:rpoj/,^?ec^row, spur ; (j)opEb),phoreo, 

 to carry.) A genus consisting of small testaceous appendages 

 fived on the posterior extremity of a species of slug. P. cor- 

 ninus. PL xiii. fig. 260. 

 PLEIODON. Conrad. Ieidina, Lam. Fam. Nayades, Lam. 

 PLEKOCHEILTJS. Guild. Atjeiotjla Caprella, Lam. Caet- 

 CHiuM undulatum. Leach. (Capeella, Nonnull.) This pro- 

 posed 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. Pig. 522, 523. 

 PLEUEOBEANCHUS. Cuv. {UXevpa, pleura, the side ; Bran- 

 chicB, gills.) Fam. Semiphyllidiana, Lam. Subaplysiacea, Bl. — 

 Descr. Internal, thin, haliotoid, slightly convex towards the 

 spiral apex ; apert\u*e entire. — Obs. This is a very light shell, 

 deUcately coloured, resembling Aplysia, but differing in the 

 integrity of the margin. P. membrauaceus. PL xii, fig. 232. 



