6. SCUTELLA. Siphon close to the side of the head. Fig. 510, 511. PHYLLONOTUS. Sw. A sub-genus of Murex, thus described: "Canal moderate; varices foliated, laciniated, compressed, or resembling leaves; inflatus. Mart. 102. fig. 980, eurystoma. Zool. Ill. ii. 100. imperialis. Ib. pl. 109." Sw. p. 296. PHYSA. Drap. A genus formed for reversed species of Limnæa, Auct. Fig. 310, P. castanea. PHYSETER. Humph. SOLARIUM, Lam. PILEOLUS. Cookson. (_A little cap._) _Fam._ Neritacea, Lam.--_Descr._ Patelliform, with the apex sub-central, straight. In the lower disc, or under surface, the centre of which is rather raised or cushion-shaped, is placed the lateral, narrow, semilunar aperture, with the outer lip marginated and the inner lip crenulated.--_Obs._ This interesting genus is known only in a fossil state. Two species are found in the upper layer of Oolite, above the Bradford clay. The spire, although internal, connects this genus in some degree with Neritina. Still there is no danger of confounding them. Fig. 332, P. plicatus. PILEOPSIS. Lam. CAPULUS, Montf. PILLAR. The usual English name for the column which forms the axis of spiral shells, around which the whorls revolve. See COLUMELLA. PINNA. Auct. (_The fin of a fish._) _Fam._ Mytilacea, Lam.--_Descr._ Equivalve, inequilateral, oblique, wedge-shaped, thin, horny; umbones terminal; hinge rectilinear, without teeth; anterior margin sinuated, to admit the passage of a byssus; posterior margin truncated, gaping; muscular impressions two in each valve; posterior large, sub-central; anterior small, terminal, sometimes double.--_Obs._ The beautiful large shells of which this genus is composed, are possessed of a large, flowing, silky byssus, of which gloves and hose have been manufactured. They have received their name from their resemblance to the pectoral fins of some fishes. Some species attain very large dimensions, and measure two feet in length. A very improbable story is told with regard to animals of this genus, namely that a certain small species of crab is in the habit of taking refuge from its enemies in the shell of the Pinna, into which it is received with great hospitality and kindness by the "_blind slug_," which inhabits it. In return for which kindness, he occasionally goes abroad to procure food for both. On his return he knocks at the shell, which is opened to receive him, and they share the supplies together in convivial security! Some species are smooth, although the greater number are imbricated or crisped outside. P. saccata, fig. 162.