PLICATULA. 85 
PLEKOCHEI'LUS. Guild. Auricula caprella, Lam. 
PLEUROBRAN’CHUS. Cuv. (Ievpa, pleura, the side; Bran- 
chie, gills.) Fam. Semiphyllidia, Lam. Sub-aplysiacea, Bl. 
Descr. Internal, thin, haliotoid, slightly convex towards the 
spiral apex; aperture entire. Obs. A very light shell, delicately 
coloured, resembling Aplysia, but differing in the integrity of 
the margin. Fig. 232, P. membranaceus. 
PLEURORHYN’CHUS. Phillips. Mrevpa, the side; puyyos, ryn- 
chus, a beak.) A genus founded upon a very singular species 
of Carpium, distinguished by the short, anterior side, and the 
elongation of the hinge line into auricular processes, which are 
truncated at the extremities. C. Hibernicum, from Black marble 
rock of Cork, which is vulgarly called Asses-hoof. C. elongatum 
(Sow. Min. Con. vol. 1.82.) may probably formpart of this genus. 
PLEURO’TOMA. Auct. (Mevpa, the side; roun, tome, a slit.) 
Fam. Canalifera, Lam. Siphonostomata, Bl. Descr. Fusiform, 
thick, generally ribbed or striated transversely; aperture oval, 
terminating anteriorly in an elongated canal; outer-lip thin, 
with a fissure near its union with the spire; columella smooth, 
nearly straight. Obs. This genus, which nearly resembles Fusus 
in other respects, may be known by the notch in the outer lip. 
The species differ in the length of the canal. Those with the 
short canals and dilated outer lip have been separated under 
the name Clavatula. Fig. 379, 380, P. marmorata, 381, P. 
strombiformis, (Clavatula. 
PLEUROTOMA’RIA. Defr. (Derived as Pleurotoma.) Fam. 
Turbinacea, Lam. Descr. Turbinated, spiral; aperture sub- 
quadrate, with rounded angles; outer lip with a deep slit near 
its junction with the spire. Obs. This genus, which is only 
known in a fossil state, abounds in inferior Oolite, Oxford clay, 
and casts are found in a limestone bed in Norway. The Scis- 
surellee differ in being very minute shells, and are not so Trochi- 
form as the species of Pleurotomaria. P. reticulata, fig. 341. 
PLICA’CEA. Lam. A family of the order Trachelipoda, Lam. 
containing the genera Tornatella and Pyramidella, to which 
may be added Monoptygma. 
PLICATED. (Pico, to fold.) Folded. Applied to spiral plaits on 
the columella of some shells. Ez. Voluta, fig. 433. Also to the 
angular bendings in the margins of some bivalve shells. Ez. 
Dendostrea, fig. 181. 
PLICA’TULA. Lam. (Plicatus, folded.) Fam. Pectinides, Lam. 
Sub-ostracea, Bl. Deser. Irregular, sub-equivalve, sub-equila- 
teral, attached by a small part of the surface of one valve, 
strongly plicated ; umbones separated by a small, external, liga- 
mentary area; hinge with two cardinal teeth in each valve, two 
approximate in one valve, received between two distant in the 
other; cartilage placed between the cardinal teeth; muscular 
