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



small, acute, appressed and does not project beyond the hinge- 

 margin. 



The radial ribs are very distinct and clean cut, thickened and 

 rounded at the summit, and separated by nearly smooth intex'vals 

 two or three times as broad as the ribs themselves. The width of 

 the ribs increases regularly from near the umbos to the margin, A 

 few intermediate ridges commence near the margin. 



The left valve is badly broken. It is, however, somewhat more 

 convex than the other, and the radial ribs are crossed by numerous 

 concentric striations, giving them a finely crenulated or beaded 

 appearance. The anterior auricle is broad-triangular, the outer end 

 slightly rounded, and with a slight incurved notch below. It has 

 about six small radial ribs, similar to those of the body of the shell. 



Raised lines of growth occur at irregular intervals. Internal sur- 

 face is smooth and lustrous, and shows the grooves corresponding to 

 the external ribs, and also a very distinct microscopic structure, but 

 is destitute of special radial lirae. 



Internally, the hinge-plate is narrow, thin, with a sharply impressed 

 submarginal groove on each end. The resilial pit is excavated in the 

 margin of the hinge itself, and the anterior auricle has internal 

 grooves corresponding to the external ribs. 



Length of the largest examples, 6™°^ ; height, 6-5'"'", 



Off the coast of Newfoundland in 67 to 72 fathoms. 



Chlamys (^quipecten) glypta Verrill. 



Pecten glyptus Verrill, Trans. Conn. Acad., v, p. 580, 1882. Ball, Proc. U. S. Nat. 

 Mus., xii, p. 248, pi. viii, figs. 2, 3, 1889. 



Pecten Tryoni Ball, Bullet. Mus. Comp. Zool., xviii, p. 438, 1887 (t. Ball). 



Plate XVI. figs. 7-1 1. 



When young this species has strong, well-defined, angular radial 

 ribs of nearly uniform size. In the old shells the grooves are 

 occupied by several small ribs, and a secondary rib develops on each 

 side of the keel of the primary rays ; the ribs are all crossed by 

 rather strong concentric sculpture (fig. 8, 11) which is sometimes so 

 coarse as to give both the ribs and grooves a rough appearance. 

 There are about three small, free pectinidial teeth in one of our 

 specimens, but Dr. Dall states tljat they are absent in his specimen 

 {P. Tryoni). It is allied to C. opercularis L., of Europe, and to G. 

 purpurata of the west coast of South America. 



Off the eastern coast of the United States in 69 to 156 fathoms. Off 

 North Carolina in 124 fathoms (Dall). This has been taken only in 

 small numbers, and mostly dead and broken. 



