68 A. E. Yerrill — Study of the family Pectinidce. 



transverse rib, besides a veiy narrow one bounding the ligamental 

 groove. In the right valve the margin, above the ligament, is in- 

 curved. The auricular crurte are feebly developed, but end in dis- 

 tinct denticles, larger in the right valve. 



In most of the species referred to this group the valves gape much 

 less at the ends than in the type-species. 



A large number of shallow-water species from all parts of the 

 world belong to this group. Many of them grow to large size. The 

 following are some of the American species: — 



C. irradians (Lam.) (pi. xvi, fig, 6 ; pi. xx, tigs. (5, 6a), from Cape 

 Cod to the Gulf of Mexico ; C. dislocata (Say), Cape Hatteras to 

 the West Indies; C. Antillarum (Rec].), West Indies ; C. nucleus 

 (Born.), West Indies; C. glyjjta Ver, (pi. xvi, iigs. 7-11), off the 

 Eastern coast of U. S. and in the West Indies, 69 to 200 fath. ; C. 

 ventricosa (Lam.), Pacific coast of tropical America ; G. p>irpurata 

 (Lam.), Pacific coast of South America; C. caurina (Gould), coast 

 of California, etc. 



Pectinella, gen. no v. Type, P. Sigsbei Dall. 



Shell small, thin, swollen, neai'ly smooth, with convex and slightly 

 unequal valves. Auricles very unequal, oblique, the anterior larger, 

 with a deep byssal notch in the right valve, but Avithout pectinidial 

 teeth ; posterior auricle small. The surface is smooth except for 

 fine lines of growth. Camptonectes sculpture is not present. The 

 texture is not hyaline. 



The only known species is Pectinella Sigsbei (Dall), Bull. Mus. 

 Comp. Zool., xli, p. 223, pi. iv, fig. 2, 1886. It was taken by the 

 Blake Exped. in the West Indies, in 158 fathoms. 



This form differs so much from all the other divisions of Pecti- 

 nidae that it seems necessary to form a new genus for it. In its 

 swollen form, it approaches some of the species of Limopsis and 

 allied forms. 



Lissopecten, new subgenus of Chlamys. Type, L. hyalinus (Poli). 



Shell slightly inequivalve, broadly rounded, not oblique, thin, 

 translucent, nearly smooth. The external sculpture consists of faint, 

 nearly obsolete radial ridges and obscure riblets, but one or both 

 auricles may have a more or less cancellated sculpture. The interior 

 sculpture consists of very distinct, simple raised ribs. Auricles 

 angular, well developed. Byssal notch deep. Pectinidial teeth 

 prominent. Mai'gin not scalloped, nearly plain and simple. 



