82 PISIDIUM. 
PHOS. Montf. Fam. Purpurifera? Lam. Descer. Turrited, thick, 
cancellated, varicose; spire pointed, not very long; aperture 
rounded or oval; outer-lip having internal ridges; columella 
with an oblique fold; canal short, forming externally a raised 
varix. Obs. The raised external surface of the canal, brings this 
genus near Buccinum, while, in general appearance, most of the 
species more nearly resemble Murex. They have, however, no 
true varices on the whorls, but merely raised bars. Fig. 416, 
P. senticosus. 
PHYLLIDIA’NA. Lam. A family belonging to the first section 
of the order Gasteropoda, Lam. containing the genera Phyllidia, 
not a shell, Chiton, Chitonellus, Patella, (including Ansates.) 
To which may be added Lottia, Gray. 
PHY’SA. Lam. A genus formed of reversed species of Limnza, 
Auct. Fig. 310, P. castanea. 
PI'LEOLUS. Cookson. (A litle 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 
and cushion-shaped, is placed the lateral, narrow semilunar aper- 
ture, with the outer-lip marginated and the inner-lip crenulated. 
Obs. This interesting genus is only known in a fossil state. 'Two 
species are found in the upper layer of Oolite, above the Brad- 
ford Clay. The spire, although internal, connects this genus in 
some degree with Neritina. Still there is no danger of confound- 
ing it with any other. Fig. 332, P. plicatus. 
PINNA. Auct. (The finof a fish.) Fam. Mytilacea, Lam. Deser. 
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 pec- 
toral fins of some fish. Some of them attain very large di- 
mensions, and measure two feet in length. Some species are 
smooth, although the greater number are imbricated or crisped 
outside. 
PILEOP’SIS. Lam. Caputus, Fer. Fig. 240. 
PIRE’'NA. Lam. A genus of freshwater shells, rejected by De 
Ferussac and other authors, who place Lamarck’s two first spe- 
cies with Melanopsis, and his two last with Melania. Fig. 316. 
P. terebralis. 
PI'SUM. Megerle. Pisip1um, Leach. 
PISI DIUM. A genus of river shells separated from Cyclas, princi- 
pally on account of a difference in the animal. The species of 
