Part 56

6. PLICATULA. Plicated, a very small area in one valve. Fig. 178.

PECTINATED. (Pecten, a comb.) Marked in a regular series of ridges.

PECTUNCULUS. (Pecten, dim.) Fam. Arcacea, Lam. and Bl.--Descr. Equivalve, sub-equilateral, orbicular, thick, covered with a velvety epidermis, striated longitudinally; ventral margin denticulated within; hinge semi-circular, with a series of small teeth on each side of the umbones, which are separated by a small triangular disc in each valve bearing the ligament; muscular impressions two in each valve, strongly marked, united by an entire palleal impression.--Obs. Linnæan conchologists have mixed this genus with Arca, from which it is, however, totally distinct, not only in the roundness of the general form, but also, and principally, in the curve of the hinge line; in fact the characters of this genus are so strongly marked that there is no danger of confounding it with any other. It does not contain many species; two or three are British. The fossil species occur in London Clay and Calcaire-grossiér. Fig. 134, P. pilosus.

PEDICLE or PEDUNCLE. (Pedunculus, a little foot.) The stem or organ of attachment of the class of shells called in the system of Lamarck "Pedunculated Cirripedes," consisting of a fleshy tendinous tube, by the lower end of which they are attached to sub-marine substances.

PEDICULARIA. Sw. A genus of "Scutibranchia," thus described: "Shell irregular, sub-patelliform; a thick, large, obsolete apex on one of the longest sides, and an internal callous rim within, on one side only; circumference undulated, irregular. P. Sicula, Sw." Sw. p. 357. Sicily. A singular shell of the nature of Calyptræa, which is found attached to corals, conforming its shape to the irregularity of their surface, and fitting closely. Ex. Fig. 513.

PEDIPES. Adanson. Fam. Auriculacea, Bl. Colimacea, Lam.--Descr. Sub-globose, longitudinal, thick, striated; spire equal to the aperture in length; aperture sub-ovate; peritreme sharp, thickened within, modified by the last whorl; columella with three strong plaits on the inner edge; outer lip with one fold.--Obs. This genus contains but one or two small recent species, which in some respects resemble Auricula, from which it is known by the thickness of its shell, and its globular form. Fig. 299, P. Adansoni. Coast of Africa.

PEDUM. Lam. (A shepherd's crook.) Fam. Pectinides, Lam. Sub-ostracea, Bl.--Descr. Irregular, inequivalve, sub-equilateral, attached by a byssus passing through a sinus in the lower valve; hinge toothless, with a triangular area in each valve, separating the umbones; ligament contained in a groove running across the area; muscular impressions one in each valve, large, sub-orbicular; both valves flat, narrow at the dorsal, broad at the ventral extremities; lower valve with raised edges overwrapping the upper.--Obs. This singular genus, of which only one species is known, differs from Ostrea, not only in shape and structure, but also in the mode of attachment, which is by means of a byssus passing through the lower valve, in Pedum, but by a portion of the outer surface of the shell in Ostrea. P. Spondyloideum (fig. 179) is the only species at present known. Moluccas.

PEDUNCLE. See PEDICLE.

PEDUNCULATED. (Pedunculus, a little foot.) Attached to external objects by a hollow fleshy tube, called the Peduncle.

PEDUNCULATED CIRRIPEDES. Lam. An order consisting of molluscs which have multivalve shells, supported on a peduncle. The genera which it contains are thus distinguished:

1. PENTELASMIS. Five valves. Fig. 34.

2. CINERAS. Five very minute valves distant from each other. Fig. 42.

3. OTION. The same, but the animal has two auricles. Fig. 43. The genus Palmina, Gray, has but one.

4. OCTOLASMIS. Shaped like Pentelasmis, but with 7 or 8 valves. Fig. 41.

5. LITHOTRYA. Five valves, peduncle scaly with a plate at the base. Fig. 39.

6. SCALPELLUM. Shape square, valves 13, peduncle scaly. Fig. 35.

7. SMILIUM. Same, but the peduncle hairy. Fig. 36.

8. IBLA. Four valves, one pair long, one pair short, peduncle hairy. Fig. 40.

9. BRISMEUS. Seven valves, even at the base. Fig. 38.

10. POLLICIPES. Principal valves in pairs, with many smaller valves at the base. This genus has been divided into Pollicipes, and Capitellum, the latter of which is founded upon Pollicipes Mitellus, Auct. Fig. 37 and 37*.

PELAGUS. Montf. A genus composed of species of AMMONITES, which have the spire covered by the last whorl, as in Nautilus and have an umbilicus. ORBULITES. Bl.

PELLUCID. Transparent.

PELORUS. Montf. POLYSTOMELLA, Bl. A genus of microscopic Foraminifera.

PELORONTA. Oken. NERITA Peloronta, Auct. Fig. 330.

PENEROPLIS. Montf. A genus of microscopic Foraminifera.

PENICILLUS. Brug. ASPERGILLUM, Auct.

PENTALEPAS. Bl. PENTELASMIS, Auct.

PENTAMERUS. Sow. ([Greek: Pente], pente, five; [Greek: meros], meros, part.) Fam. Brachiopoda, Lam.--Descr. Equilateral, inequivalve; one valve divided by a central septum into two parts; the other by two septa, into three parts; umbones incurved, imperforate.--Obs. Dalman remarks upon his genus Gypidia, that it is most probably identical with PENTAMERUS, Sow. but rejects the name for two reasons; 1st. That it has already been applied to a class of insects; 2nd. He disputes the fact of the shell being quinquelocular, i.e. not counting the triangular foramen in the hinge of the larger valve as one of the divisions. Fig. 212, 213.