70 A. E. Yerrill — Study of the family Pectinidm. 



oblique, longitudinal fissure, so that the lobes can be spread apart or 

 closed, at will, thus resembling somewhat the foot of Ledidae. 

 Toward the base, on the anterior side, there is also a short, deep 

 byssal slit, terminating at a prominent tubercle about the middle of 

 the front side. 



Cyclopecten, gen. nov. Types, Pecten pustulosus Verrill ; P. imhrifer 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 lamellae, 



Fig. I. 



Figure 1. — Cyclopecten pustulosus Y . ; a, left, b. right valve, natural size. 



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, jDustules, or points, and also concenti'ic 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; bj^ssal notch well defined ; few or no pectini- 

 dial teeth. Cardinal folds single, rather feebl}" developed, often 

 cross-lined. Eyes few. Byssus small, and of few threads. 



The species of this group have usually been referred to Pseuda- 

 mtisium, but they difi^er 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 flex- 

 ure of the lower one, and in which the auricles are small and nearly 

 equal. 



This genus includes a large number of small species, raosth' from 

 deep water. Among these are the following: C. imhrifer (Lov.), 

 northern coasts of Europe ; C. pustulosus (Ver.) (cut, fig. 1), (pi. 

 xix, figs. 3, 4); C. subimbrifer (V. and B., see p. 84), 121 fath.; C. 

 leptaleus (Ver.), 142 fath.; C. nanus V. and B.; (pi. xvi, figs. 12- 

 12c), the last four are from deep water off the eastern coast of the 



