56 A. E. Verrill — Study of the family Pectmidm. 



Synospis of the generic and sectional groups of Pectinidce. 



After the previous exjjlanations it will, perhaps, be useful to give, 

 in a brief summary, the divisions of the old genus Pecten that seem 

 worthy of recognition, either as genera, or subgenera, or sections, 

 with their original types, so far as they can be fixed. The groups 

 are here arranged in the order of their sequence in date, under the 

 binomial system. Several fossil genera are here included, for com- 

 parison with modern forms, but some fossil groups are omitted for 

 lack of accurate knowledge of their characters. 



Pecten Miiller, 1776. Type, P. maximus Linnb. 



Pecfew (1st section) Klein. 1753 + Vola. 



Pecten Muller, Prod. Zool. Dan., 1776 {pars); Pecten Bolten. 1 798 (rest); DaCosta. 

 1778; Cuvier, 1793; Lamarck. Syst., 1801. 

 Janira Schumacher, 1817: Dall {pars) 1886; Fischer, 1887. 



Vola H. and A. Adams (after Klem), 1858 ; Stoliczka, 1871 ; Zittel. 1881. 



Vola + Janira Chenu, 1862. 



Since Bolten, in 1798, definitely restricted the name Pecten to this 

 group, as explained above, his restriction has precedence over that of 

 Schumacher. The shells are generally large and heavy, and the 

 valves are very unequal even when very j^oung. The right valve is 

 strongly convex Math a large and much incurved umbo and beak, 

 Avhile the left valve is flat or even concave. It is usually smaller 

 than the right, and shuts closely inside of its scalloped margin, and 

 its umbo is nearly or quite obsolete. The auricles are of moderate 

 size and not oblique, and in the right valve they are strongly convex 

 or excurved in the middle. This valve has a sinuous, excurved bys- 

 sal notch, with obsolete pectinidial teeth. The opposed auricles of 

 the left valve are deeply incurved to fit closely against the others. 

 The hinge-plate in both valves has usually two or three divergent 

 ribs on each end, of which the innermost is usually the strongest and 

 most divergent. The resilium in the right valve rests on a shelf-like 

 chondrophore inside the hinge-margin. A distinct tooth-like tubercle 

 exists below each auricle within the margin of both valves. The 

 surface of both valves has strong radial ribs interlocking at the mar- 

 gin. Internally there are angular, thickened and fluted radial ribs, 

 opposite the external grooves ; these ribs become more prominent 

 and bicarinate or fluted near the margins. 



Some of the species are known to be hermaphrodite. The foot of 

 P. tnaxinms is described as spatulate at the end. 



