A. E, Verrill — Study of the family Pectinklce. 53 



Pallial eyes and tentacles. — All the larger forms have very numer- 

 ous marginal, pallial tentacles, varying in size and length and gener- 

 ally arranged somewhat in relation to the size of the corresponding 

 radial ribs and grooves of the shell. There is a separate inner row 

 or rows of *' guard tentacles " on a raised inner pallial fold (pi. xx, 

 figs. 5, 6, 7, 8a). The marginal tentacles are accompanied by a series 

 of well-formed pallial eyes, very lustrous while living, and having a 

 crystalline lens. These eyes in the larger species are numerous, and 

 differ in size, the larger ones corresponding to the primary ribs, the 

 smaller ones alternating in pretty regular order, according to the 

 sculpture (pi. xx, figs. 6, 6a). The tentacles and eyes extend all the 

 way around the margin of the mantle, beyond its free portions and 

 even to the end of the auricles, which usually gape at the ends to 

 give room for these organs. The tentacles and eyes are more or less 

 reduced in the anal region. In some of the small deep-sea forms 

 there are but few eyes, and in some cases they are not pigmented 

 (at least in alcoholic specimens). 



Remarks on the Nomenclature of Pectinidce. 



There is still so much diversity of opinion in recent malacological 

 works concerning the nomenclature of the genera and subordinate 

 groups of PectinidfB that a brief review of the subject seems war- 

 ranted. In general, the subdivisions here adopted correspond in 

 most cases pretty neai'ly with those defined by Stoliczka,' with 

 some additional ones. But as Stoliczka considered that the ante- 

 binomial names of Klein (1753), should take precedence of those 

 given under the binomial rules, there is considerable disparity in 

 the nomenclature. Mr. Dall" has more recently discussed several of 

 these groups. . He followed the more generally adopted rules respect- 

 ing priority of names, and therefore his conclusions were more 

 nearly in accord with those adopted by me. 



The most fundamental and important question to be settled in the 

 nomenclature of this family is the correct application of the name 

 Pecten to one of the restricted modern genera. The old genus 

 Pecten has been divided by various authors into several genera, sub- 

 genera, and sections, of very unequal value. Many of them were 

 not definitely defined by their authors, and for several no definite 



' Ferd. Stoliczka, Mem. Geol. Survey of India. Cretaceous Pelecjpod Fauna of 

 southern India, Vol. iii, pages 423-430, 1871. 



2 W. H. Dall, Bull. Mus. Comp. Zool., xii, pages 210-219, 1866. 



