The shell of the _Pecten_ is in general nearly circular, more or less elongated, and terminated towards the summit in a straight line, forming a sort of triangular appendage called the ear, to which the hinges are attached. The valves are very regular, but with no resemblance to each other. In some species, the shell of which is closely shut, the lower valve is more or less convex than the upper one. In others, both valves are convex. The hinge is without teeth, and the ligament, which is intended to close the shell, is inserted into a triangular depression or dimple. The retractile muscle is unequal, and nearly central. The valves are not nacred inside, and are formed on their exterior surface of numerous fluted channels, which spring from a lobe more or less pointed at the summit, diverging towards the circumference. The edges are sometimes smooth, as in the Watered Pecten (_P. pseudamussium_, Fig. 175), but more frequently they are formed in strips or scales, as in the Smooth-shelled Pecten (_P. glaber_, Fig. 176). Upon the whole, however, the Pectens are very variable, but always elegant in form; the colours are frequently lively and brilliant. In PL. XIV., some of the most striking forms are represented, as in Fig. I., the Ducal Mantle (_Pecten pallium_), an inhabitant of the Indian Ocean, remarkable for its elegant form, its twelve radiating stripes, diverging towards the circumference, the horizontal furrows of its salient scales, and the striking distribution of its white spots upon a bed of red and brown marble; Fig. II., the Purple Pecten; Fig. III., the Coral Pecten; Fig. IV., the Tiger Pecten; Fig. V., the Foliaceous Pecten; and Fig. VI., the Northern Pecten. [Illustration: Fig. 175. Pecten pseudamussium (Chenu).] [Illustration: Fig. 176. Pecten glaber (Linnæus).] The animal which inhabits the Pecten shell has the general form of the oyster, differing however from it in a remarkable manner. The edges of the mantle are furnished with multiplied fringes of simple tentacles, between which we find other tentacular appendages a little thicker, each terminating in a sort of small pearl, vividly coloured, to which is attached a nervous thread, which has been taken for an eye. Another difference: the branchiæ, in place of being connected by a striated lamina, as is the case in the oyster, are cut into parallel capillary filaments, forming a free and floating fringe, and the mouth is surrounded by salient many-cleft lips. [Illustration: PLATE XIV.--Pectinidæ. I. Pecten pallium. (Linn.) II. Pecten purpuratus. (Lamarck.) III. Pecten foliaceus. IV. Pecten tigris. (Lamarck.) V. Pecten nodasus. (Linn.) VI. Pecten islandicus. (Chemnitz.) ]