PECTEN. Brug. (_A comb._) _Fam._ Pectenides, Lam. Subostracea, Bl.--_Descr._ Inequivalve, ribbed longitudinally, nearly equilateral, with a triangular auricle on each side of the umbones; hinge linear, destitute of teeth, having a central pit containing the cartilage; muscular impressions one in each valve, large, sub-central.--_Obs._ This genus of beautiful shells, to which the well known Scallop belongs, contains numerous species, some of which are found in the British Seas. The Hinnites Pusio (P. Pusio of some authors) has been separated on account of the irregularity of the external surface of one valve. Fig. 171 to 173. PECTENIDES. Lam. A family belonging to the second section of the order Conchifera Dimyaria, Lam. including the following genera. 1. PECTEN. Unattached, including _Decatopecten_ and _Hinnites_. Fig. 171, 172, 173. 2. LIMA. Unattached, gaping, Fig. 174. 3. PLAGIOSTOMA. Unattached, with an area between the umbones. Fig. 176. 4. DIANCHORA. Attached by the point of the umbo. Fig. 175. 5. SPONDYLUS. Attached, irregular, a triangular area in one valve, divided by a slit. Fig. 177. 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.