POSTERIOR. 251 



shells, viz. Orthocerata, Lituacea, Cristacea, Sphserulacea, Ea- 

 diolata, Nautilacea, Ammonacea. Eig. 463 to 484. 



POLTTEOPA. Sw. A genus of Scolyminse, Sw. thus de- 

 scribed : " Buceiniform ; "but the base narrow, and ending in a 

 straight and contracted, but rather short, channel ; spire longer, 

 or as long as the aperture ; exterior foliated, or tuberculated j 

 inner lip flattened, as in Purpura; basal notch small, oblique j 

 no iatemal channel ; crispata. En. Meth. 419, f. 2. Chem. 187, 

 f. 1802. Capilla, Pennant, pi. 72, f. 89, imbricata. Mart. 122. 

 f. 1124. ? rugosa. Chem. f. 1473-4." Sw. p. 305. PI. xxvi. 

 fig. 546. 



POLTXENES. Montf. A genus of microscopic Eoraminifera. 



POMATIA. aesner. (Gray, Syn. B. M. p. 133.) A genus of 

 the family of " Cyclostomidse," described as having " an elongated 

 shell with reflexed lips, and a horny spiral operculum." Also a 

 sub-genus of Snails, containing Helix pomatia, Auct. (Grray's 

 Turton, p. 135.) 



POMATIAS. Hartman, 1821. Species of Cyclostoma, of a tur- 

 rited tapering form, with reflex lips. Cy. patula, Thesaurus 

 Conchyliorum. PI. xxviii. flg. 171. 



POMTJS. Humph. Part of Amptjllaeia, Lamarck. 



POECELLANA. Adanson. Maechiojlla, Auct. Monograph, 

 Thes. Conch. PI. viii. 



POEODEAG-US. Montf. A genua composed of species of Belem- 

 nites, placed by De Blainville in the section characterized as 

 swelled near the apex, and straightened towards the base. 



POEONIA. Eecluz. See.KELLiADiB. P. rubra. PI. xxvii. fig. 

 568. 



POSIDONIA. Brong. A genus formed on the cast of a bivalve 

 sheU, common on schists from Dillemberg. 



POSTEEIOE. {After, behind.) The posterior or hinder part of 

 a bivalve shell, is that in which the siphonal tube of the animal 

 is placed. It is known in the shell, by the direction of the curve 

 in the umbones, which is from the posterior towards the anterior ; 

 also by the ligament, which is always placed on the posterioi- 

 part of the hinge, when it exists only on one side of the um- 



