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Cyclopecten, gen. nov. Types, Pecten pustulosus Verrill; P. imbrifer Loven.



PLATE XVI. fig. 1. PLATE XIX. figs. 1-4.



Shells thin, rounded, scarcely oblique, with symmetrical auricles and simple margins. The two valves are unlike in sculpture. The right valve is a little flattened and upturned at the flexible margin, so as to fit tightly against the upper valve. The thin lower valve has, in the typical species, regular, thin, elevated, concentric lamellæ, which aid in the adaptation of the edge to that of the upper valve; the margin is usually flattened or bevelled. The upper (left) valve is radially sculptured, rarely smooth; it usually has radial rows of arched scales, pustules, or points, and also concentric raised lines; it is sometimes cancellated. No radial ribs, nor interlocking points at the margin. Auricles well developed, subequal, angulated and well-defined at both ends; byssal notch well defined; few or no pectini­dial teeth. Cardinal folds single, rather feebly developed, often cross-lined. Eyes few. Byssus small, and of few threads.


The species of this group have usually been referred to Pseuda­musium, but they differ widely from the typical forms of that group, such as P. exoticum, P. dispar, etc., in which the valves are of nearly equal size, with simple edges that come evenly together without flex­ure of the lower one, and in which the auricles are small and nearly equal.


This genus includes a large number of small species, mostly from deep water. Among these are the following: C. imbrifer (Lov.), northern coasts of Europe; C. pustulosus (Ver.) (cut, fig. 1), (pl. xix, figs. 3, 4); C. subimbrifer (V. and B., see p. 84), 121 fath.; C. leptaleus (Ver.), 142 fath.; C. nanus V. and B.; (pl. xvi, figs. 12– 12c), the last four are from deep water off the eastern coast of the United States; C. reticulus (Dall); C. simplex Ver. (pl. xvi, fig. 1, xix. figs. 1, 2) and C. Culebrensis (Smith), 390 fath., are from the West Indies; C. Murrayi (Smith), 1400 fath., off Australia; C. clathratus (Mart.), 120 fath.; C. subhyalinus (Smith), 400 fath.; and C. distinctus (Smith), 100 fath., from the Antarctic regions; C. Ker­madeciensis (Smith), 600 fath., off Kermadec I.


C. orbicularis (Sowerby), which occurs on the west coast of Africa, living among, and usually attached to, floating fucoids (Sar­gassum, etc.), near the shore, appears to belong to this genus. It has concentric sculpture on both valves; that on the left forms raised scale-like lamellæ. The shell is hyaline. The valves close tightly by the upturning of the edge of the right one. According to Dr. Charbonnier (Journ. de Conch., ser. II, vol. iv, p. 261) this species swims about very actively, but attaches itself very firmly and quickly (in 15 minutes), to floating alga by a byssus of several threads. When at the bottom of the glass vessel, it creeps about by means of its foot.”



(Verrill, 1897: 70-71)


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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