236 PEEIOSTEACUM . 



two septa, into three parts ; umbones incurved, imperforate. — 

 Obs. Dalman remarks upon this genus G-ypidia, that it is most 

 probably identical with Pentamerus, Sow. ; but rejects the 

 name for two reasons ; 1st. That it has already been applied to 

 a class of insects ; 2nd. He disputes the fact of the shell being 

 quinquelocular, i. e. not counting the triangular foramen in 

 the hinge of the larger valye as one of the divisions. PI. xi. Pig. 

 212, 213. 



PEIS'TELASMIS. Leach. See Lepas. (JltvTE,pente,^Ye;t\aaixa 

 elasma, plate.) Order. Pedunculated Cirripedes, Lam. — Descr. 

 Compressed, conical, composed of five valves ; lower lateral pair 

 sub-trigonal ; upper lateral pair elongated, sub-quadrate ; dorsal 

 valve accurate, peduncle elongated, smooth. Pound on floating 

 wood in the sea. — Obs. This genus should have been described 

 under the name Lepas ; it is known from all others of the order 

 by the number of valves. Pentelasmis is the genus Anatifera 

 of Lamarck. Lepas anatifa, Linn. Possil species of this 

 marine genus are found in the Calcaire-grossier of Paris, and in 

 other similar beds. P. Isevis. PI. ii. fig. 34. 



PENULTIMATE WHOEL. The last whorl but one. 



PEEA. Leach. A genus composed of Ctclas amnica, and other 

 similar species. PL xxiv. fig. 500. 



PEEDIX. Montf. Dolitjm Perdix, Auct. 



PEEPOEATED. (Perforatus.) Bored through, as the apex of 

 Pissurella, fig. 245, and Dentalium, fig. 2. 



PEEPOEATION. {Perforo, to bore or pierce.) A round open- 

 ing, and having the appearance of being bored, as in Haliotis, 

 fig. 338. Sometimes the term is applied to an umbilicus which 

 which penetrates a shell through the axis to the apex, as Eulima 

 splendidula, fig. 348. 



PEEIBOLUS. Brug. A genus founded upon young specimens 

 of CYPKiEA, with their outer lips not formed. 



PEEIOSTEACUM. A name used by Mr. Gray to signify the 

 substance which covers the outer surface of many shells, called 

 the Epidermis by most conchological writers. " Drap Marin" is 

 the name given to this substance by Prench Naturalists. 



