A. E. Verrill — Study of the family Peclinidce. 61 



parallel with the marginal ligaraental groove. It is usually cross- 

 incised. The byssal notch is small and the pectinidial teeth are up 

 to five in number, or sometimes lacking. Some of the species, if 

 not all, show the fine divergent " camptonectes-sculpture," on one or 

 both valves, especially when young. 



This group was adopted by H. and A. Adams, from Klein, but 

 they gave no adequate definition, and designated no special type. 

 They gave an alphabetical list of twenty-one species. Among these 

 are rejiresentatives of several diverse groups {Amusium, Cyclopecten, 

 Chlamys, Palliolum or Gamptonectes, etc.). If these incongruous 

 groups be eliminated, those that remain may be referred to the 

 group characterized above, with such species as P. dispar (Lam.) 

 and P. exoticum (La,m.) =pseiidcwmsmm (Sowerby) as typical forms, 

 whether they be distinct species or not. 



Klein, himself, referred to his genus certain fossil shells which, as 

 he stated, differ from Amiisiwn only in lacking ribs and grooves. 

 He also cited one of Lister's species, with his diagnosis, but he gave 

 it no name. His figure (copied from Lister) is a crude representation 

 of a variegated species, like P. exoticum or P. dispar. 



Although I do not, personally, consider Klein's type as of any 

 importance in the limitation of the group, it may satisfy others to 

 know that his tj^DC is the same as that adopted above. 



Chenu, 1861, gave as " examples " three species : P. dispar (Lam.); 

 P. pseudamusium (Lam.) ; P. glaher (Linne). The first two are 

 typical, but the last belongs to another section. 



Stoliczka gave a definition of the group, with P. exoticum as the 

 type. He also cites P. corneiim, P. hyalinum., P. tigrinum, and P. 

 nutans as typical examples. Some of these belong in diverse groups. 



Zittel, in 1881, gave P. glahrum and P. hyalinum, as types. 



From the incongruous species included in this group by H. and A. 

 Adams and others, we may well separate those that have internal 

 ribs, and also the thin, delicate, deep-sea species, with unlike 

 valves, the right valve usually having strong concentric sculpture. 

 For this last group I have established the genus Cyclopecten. Of 

 the American species, our common large New England species, P. 

 Glintonius or Magellanicus (Lam.) resembles this subgenus. It is 

 similar to the typical species in form of shell and auricles. It differs 

 mainly in gaping at both ends and having stronger radial sculpture 

 on the upper valve. But the character of the shell and the form of 

 the foot are so peculiar as to warrant the institution of a special 

 geniis or subgenus for its reception (see p. 69). 



