A. E. Verrill — Study of the family Pectinidm. Vl 



United States; G. retlcidus (Dall); C. simplex Ver. (pi. xvi, fig. 1, 

 xix, figs. 1, 2); and C. Culehrensis (Smith), 390 fath., are from the 

 West Indies; G. Murrayi (Smith), 1400 fath., off Australia; G. 

 clathratus (Mart.), 120 fath.; G. suhhyalinus (Smith), 400 fath.; and 

 G. distinctus (Smith), 100 fath., from the Antarctic regions ; G. Ker- 

 madeciensis (Smith), 600 fath., off Kermadec I. 



G. orbicularis (Sowerby), Avhich occurs on the west coast of 

 Africa, living among, and usually attached to, floating fucoids {Sar- 

 gassum, 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 lamellae. 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. 11, vol. iv, p. 261) this species 

 swims about very actively, but attaches itself very firmly and 

 quickly (in 15 minutes), to floating algse by a byssus of several 

 threads. When at the bottom of the glass vessel, it creeps about by 

 means of its foot. 



Hyalopecten, gen. nov. Type, H. undatus V. 



Plate XVIII. fig. 5. 



Shell compressed, thin, hyaline. Valves nearly equal, with con- 

 centric undulations or corrugations, affecting the entire thickness; 

 margins simple ; sculpture none, or consisting of fine radial lines on 

 one or both valves, without camptonectes sculpture. Hinge-plate 

 thin and nearly plain ; auricles well developed, unequal ; byssal notch 

 distinct. 



The possible relations of this group to Syncyelonema were dis- 

 cussed on page 63. 



The species known to me are as follows : II. dilectus V. and B., 

 from 1813 fath., off Martha's Vineyard ; II. fragiUs (Jeff.), from 

 northern Europe and the Arctic Ocean, and off the U. S. coast, in 

 578 to 1525 fath.; II. undatus Ver., off the U. S. coast, in 1423 fath.; 

 and H. pudicus Smith, off Marion I., in 1375 fath. 



Protamusium, gen. nov. Type P. demissum (Phil.). 



Body of shell disk-like, nearly circular, and compressed, valves 

 thin, with fine regular concentric grooves and fine raised lamellre. 

 Auricles short, but distinct, angular, not oblique, nearly equal, not 

 prolonged dorsally ; no byssal notch. 



This division is proposed for certain mesozoic shells that closely 

 resemble Amusium in form, but appear to be entirely destitute of 

 the internal radial ribs, so characteristic of the latter. It differs 



