62 A. E. Verrill — Study of the family Pectiiiidm. 



Of the European species examined by me, P. similis (pi. xvii, figs. 



8, 8a) seems to belong to the restricted group. Allied species occur 



in the Tertiary and Cretaceous formations. 



• 

 Camptonectes Meek, 1864. Type, P. lens Sowerby. 



Camptonectes Stoliczka, 1871 ; Zittel, 1881 (type, arenatus Goldf.). 



Shell subovate, plain, not corrugated, and without strong radial 

 ribs ; margin nearly plain. Valves subequal. Auricles unequal ; 

 byssal notch well developed. Surface of the shell covered with fine, 

 obliquely divergent, curved, crenulated or vermiculated riblets with 

 intervening, narrow, punctate grooves. 



The curious vermiculated sculpture is not peculiar to this division, 

 but is more or less obvious on the shells of some species of Pseuda- 

 musium, and on species of several other groups, both with and with- 

 out radial ribs. It is a structural feature that runs obliquely across 

 the ribs and grooves. Most of the species ai'e mesozoic fossils. 



The recent Pecten striatus and P. tigrinus Lam. of Europe, apjDar- 

 ently belong to this group, and P. Testm might, also, well be referred 

 to it. It is generally regarded as only a section of Pseudamusinm. 



Entolium Meek, 1864. Type, D. cornutum Queenst. 



Body of shell rounded, not oblique ; valves thin, nearly equal. 

 Sculpture delicate. Auricles well developed, those of the right valve 

 prolonged dorsally beyond the hinge-line in the form of angular 

 lobes. Byssal notch obsolete. Apparently there are no internal ribs 

 or lii'ffi. This genus appears to be allied to Amusiicm, which it 

 resembles in the form of the disk, shortness of the auricles, absence 

 of byssal notch, and apparently in the texture of the shell. But it 

 diilers in lacking the internal lirge, and especially in the dorsal pi'cf- 

 longation of the auricles. The last character distinguishes it, also, 

 from Protamusium V., to which it appears to be still more closely 

 related. 



Syncyclonema Meek, 1864. 



Type = P. rigida Meek and Hall, Mem. Amer. Acad. Arts and Sciences, Boston, vol. 

 V, p. H81, pi. i, figs. 4, a, h, c=P. Halli Gabb. j 



Syncyclonema Meek, Smithsonian Check List Cret. Fossils, p. 31, 1864. 



The type of this group is a small, poorly preserved, thin shell, with 

 concentric grooves or undulations on at least the " left or inferior '* 

 valve, and with radial strife on the other. The shell is compressed, 

 obovate, higher than long, not oblique, gradually narrowed to the 



