A. E. Verrill — Study of the family PectinidcB. 95 



Figure 4. — The same. Diagramatic view of gill-filament of adult; a, direct border; a', 



reflected border ; s, septum uniting the two parts of about every fifteenth filament ; 



6^, blade. 

 Figure 5. — The same. Diagram of section through shell (s) and adductor muscle (ad)\ 



I, resilium ; m, mantle ; miu, guard or inner reflected edge of mantle ; gt, guard 



tentacles; t, marginal or pallial tentacles; e, ocelli. 

 Figure 6. — The same. Yiew of the interior when the shell and mantles are spread 



open ; about twice natural size ; a, mouth ; b, rectum and anus ; c, abdominal 



mass ; d, labial palpi ; e, oral tentacles ; /, foot ; g, inner gill, showing reflexed 



margin ; m, inner surface of mantle ; m', its reflexed inner margin or guard, and 



guard tentacles. From an alcoholic specimen. 

 Figure 6a. — The same. Portion of the mantle margin more enlarged : o, o', primary 



and secondary ocelli ; t, t', primary and secondary tentacles. 

 Figure 7. — Chlaviys (Placopecteu) Clintonius. Front view of a small living and active 



specimen about one-half natural size ; on, inner mantle margin or guard. 

 Figure 8. — The same. Foot of a larger alcoholic specimen, x 2 ; r, byssal groove ; s, 



terminal bilobed disk. 

 Figure 8a. — The same. Portion of the mantle-margin of an alcoholic specimen, x 4: ; 



m, inner surface of mantle, showing blood spaces and nerves ; m', reflexed 



inner margin; m", guard tentacles ; #, marginal pallial tentacles ; o, ocelli. 

 Figure 9. — Chlamys Islandica. The foot of an alcoholic specimen, x 6; r, byssal 



groove ; s, terminal slit or groove. 

 Figures 1-5 of this plate are copied from Dr. Jackson ; fig. 7 was drawn by J. H. 



Emerton ; the rest are by A. Hyatt Yerrill. 



Plate XXI. 



Figure 1. — Chlamys (Placopecten) Clintonius. Part of animal of an alcoholic speci- 

 men, x 6 ; a, mouth ; e, oral tentacles ; cZ, d', outer and inner labial palpi ; g, ante- 

 rior end of gill. 



Figure la. — The same, a part of one of the oral tentacles, more enlarged, to show 

 mode of branching. 



Figures 2, 2a. — The same. Right and left valves showing muscular scars, f natural 

 size ; a, a, scars of adductor ; a', portion of adductor with finer fibers ; b, pallial 

 line ; c, row of small pallial scars, of irregular occurrence ; d. d, more or less 

 lobed dorsal margin of adductor scar ; the pedal muscle is attached obliquely to 

 the adductor muscle of the left valve at d, in fig. 2a ; e, e', special pallial muscles 

 below the auricles (subauricular muscles), situated in the region where the 

 pallial guard become narrow and the guard-tentacles obsolete ; n, byssal notch ; 

 I, ligament; t, transverse cardinal rib; r, resilium. 



Figures. — Chlamys Islandica. Part of animal, x 6; a, mouth; e, oral tentacles; d, 

 d', outer and inner labial palpi ; g, anterior end of gill ; r, byssal groove of foot ; 

 5, terminal slit of foot. 



Figure 4. — Pallium 'plica. Hinge of right valve, x 5. 



