80 PHARETRIUM. 
in the Calcaire-grossi¢r of Paris, and in other similar beds. 
Fig. 34, P. levis. 
PER’DIX. Montf. Do.ium Perdix, Auct. 
PERFORA’TION. (Perforo, to bore, to pierce.) A round open- 
ing, having the appearance of being bored, as in Haliotis, fig. 
338. Sometimes the term is applied to an umbilicus which pe- 
netrates a shell through the axis to the apex, as Eulima splen- 
didula, fig. 348. 
PERIBO’LUS. Brug. A genus founded upon young specimens 
of Cyprez, with their outer lips not formed. 
PERIOSTRACA. See EpipErmis. 
PERIPLO’'MA. Schum. Osreropssma, Desh. Rupicona. Fl. de 
Belvue. Anatina rupicola, Lam. Fig. 72, P. inequivalvis. 
PERISTO'MATA. Lam. A family belonging to the first section 
of the order Trachelipoda, containing the genera Valvata, Palu- 
dina, Ampullaria (including Lanistes, Montf.) Fig. 318 to 322. 
PERLAMA’TER. Schum. (Mother of Pearl.) Me.Eacrina 
Margaritifera, Lam. The pearl oyster. 
PERNA. (“Perne concharum generis, Plin.” ) Fam. Malleacea, 
Lam. Descr. Sub-equivalve, irregular, compressed, foliaceous ; 
hinge straight, linear, composed of a series of transverse parallel 
grooves containing the cartilage and intermediate spaces bearing 
the ligament; anterior margin with a sinus for the passage of a 
byssus; posterior ventral margin oblique, attenuated. Obs. This 
genus is known from Crenatula by the straightness, number and 
regularity of the grooves in the hinge and the sinus, for the pas- 
sage of the byssus. Fig. 166, P. Ephippium. 
PERSI'CULA. Schum. A genus formed of Mareinexia Persi- 
cula, Auct. and other species having the spire concealed. Fig. 
438. 
PER’'SONA. Montf. (Mask.) A genus composed of Trrron 
Anus, Auct. and similar species. Fig. 401. 
PETRI'COLA. Lam. (Petrus, a stone ; cola, an inhabitant.) Fam. 
Lithophagi, Lam. Deser. Equivalve, inequilateral, transversely 
ovate or oblong, rather irregular; anteriorside rounded, poste- 
rior side more or less attenuated, slightly gaping ; hinge with two 
cardinal teeth in each valve; muscular impressions two in each 
valve; pallealimpression entire; ligament external. Obs. The 
Petricolee are found in holes made by the animal in rocks, Madre- 
pores, &c. They maybe known from Saxicava, by the regu~ 
larity of their form and the teeth on the hinge. Fig. 91, 92. 
PHARA’MUS. Montf. Lenticuntina, Bl. A genus of micro- 
scopic Foraminifera. 
PHARE’TRIUM. Konig. (faperpedv, pharetreon, a quiver.) Deser. 
A testaceous body composed of two conical sheaths, one within 
the other, perforated at the apex, and joined together near the 
oral margin. P. fragile, fig. 3. 
