4. VAGINULA. Straight, widened in the centre; apex pointed. Fig. 225. 5. CUVIERIA. The same; apex blunt. Fig. 223. 6. CLEODORA. Aperture with three spines; apex recurved. Fig. 221. 7. HYALÆA. Vaulted, open extremity, three-cornered; apex tridentate. Fig. 226. PTEROPODA. Bl. The second family of Nucleobranchiata, Bl. the shells of which are described as symmetrical, extremely thin, transparent, longitudinally enrolled, either forwards or backwards. The animals are remarkable for a pair of broad, flat, natatory organs or membranaceous fins, from which the family derives its name. It contains, in the system of De Blainville, the genera Atlanta, Spiratella, and Argonauta, to which may probably be added PHARETRIUM, König; ENTALIS, Defrance. PULLASTRA. Sow. _Fam._ Conques Marines, Lam.--_Descr._ Equivalve, ovate or oblong, transverse, inequilateral; hinge with three diverging cardinal teeth in each valve, notched at the terminations; muscular impressions two in each valve; palleal impression having a large sinus; ligament external, partly hidden by the dorsal margin.--_Obs._ This genus includes the Venerirupes of Lamarck, and several species of his Veneres, they are found in the sand on the shores of temperate and tropical climates. Fig. 120, P. textile. PULMONOBRANCHIATA. Bl. The first order of the first section of Paracephalophora monoica, containing the families Limnacea, Auriculacea, and Limacinea. PULVINITES. Defr. (_Pulvinus_, a cushion.) _Fam._ Malleacea, Lam.--_Descr._ Sub-equivalve, inequilateral, compressed, thin, slightly gaping posteriorly; one valve flat, the other rather concave; hinge linear, short, divided into perpendicular grooves; muscular impressions two, one sub-central, the other above it, nearer the hinge.--_Obs._ This fossil shell is imperfectly known, and it is difficult to give a sufficient reason for separating it from Perna. It comes from the Baculite limestone of Normandy. Fig. 170, P. Adansonii. PUNCTATED. (_Punctatus_, spotted or dotted.) For example, see Conus Nussatella. Fig. 460. PUNCTICULIS. Sw. A sub-genus of "Coronaxis," Sw. (Conus) described in Swainson's Malacology, page 311. PUNCTURELLA. Lowe. CEMORIA, Leach. PUPA. Auct. _Fam._ Colimacea, Lam.; Limacinea, Bl.--_Descr._ Cylindrical, generally ribbed; spire long, obtuse, composed of numerous slowly increasing whorls; aperture sub-quadrate, rounded anteriorly, entire; outer lip thickened; columella plaited.--_Obs._ This genus is composed of land shells very variable in form, differing from Bulinus in the numerous slowly increasing whorls of the spire, and in the plicæ on the columella, and from Clausilia in the want of a clausium. Britain, Southern Europe, East and West Indies, Mexico, &c. P. Uva. Fig. 291.