260 PTKGOMA. 



- branchiata, Bl. the shells of which are described as nearly always 

 regular, rarely otherwise, nearly always equivalve, gaping at 



• both extremities ; hinge incomplete, the teeth becoming gradu- 

 ally obsolete ; two distinct muscular impressions ; palleal im- 



■ pression very flexuous posteriorly. This family is divided into : 

 Section 1. Ligament internal ; Pandora, Thracia, Anatina, Mya, 

 Lutricola. Section 2.. Ligament external ; Psammoeola, Sole- 

 tellina, Solen, Sanguinolaria, Solenocurtus, Solinomya, Panopsea, 



• Grlycimeris, Saxicava, Byssomya, Ehomboides, Hiatella, Bas- 

 trochaena, Clavagella, Aspergillum. 



PYEAMIDAL. {Pyramidalis.^ Eesembliug a pyramid in form. 

 Ex. Cerithium Telescopium, fig, 378. 



PYEAMIDELLA. Lam. {A little pyramid.) Fam. Pliacea, 

 Lam. Atjrioulaoea, 'El.—Bescr. Pyramidal, smooth, po- 

 lished ; spire long, pointed, composed of numerous whorls ; 

 aperture small, modified by the last whorl, rounded anteriorly ; 

 outer lip slightly expanded ; columella tortuous, with several 

 folds. This is a genus of small, polished, mariae shells, Pyra- 

 midella Terebellum. PI, xv, fig. 342. 



PYEAMIS. Sehum. 1817. Testus, Montfort, 1810. Trochus 

 Obeliscus. Lamarck. 



PyEAZTJS, Montf. Part of the genus Potamis, Brongniart. 



PTEELLA, Sw. A genus consisting of Turbinella Spirilla, 

 Auct. and similar species, having a long channel, a pyriform 

 outliae, and one strong plait at the base of the columella, the 

 apex of the spire is enlarged. P, SpiriUus, fig. 344. (The 

 proper term would be Spirilla.) PI. xxxi. fig. 550. 



PTEIPOEM. (Pyrum, a pear ; forma, shape.) Shaped like a 

 pear, i. e. large and rounding at one end, and gradually tapering 

 at the other. Ex. Pyrula, fig. 390. 



PTEGrO. Defr. A genus of microscopic Poraminifera. 



PTEGOMA. Auct. (Ilvpyos, pyrgus, a tower.) Order, Sessile 

 Cirripedes, Lam. — Descr. Composed of a single conical, hollow 



• paries, with a small aperture closed by an operculum of four 

 valves, and supported npon a cup-shaped base. — Obs. The genera 



- into which Leach has divided this genus are Pyrgoma, Adna, 



