216 BULLETIN OF THE 



Subgenus PECTEN s. s. 

 Pecten magellanicus Gmelin. 



P. magellanicus Gmelin {Ostrrn), S. N., p. 3317, 1788. 



P. Clintonius Say ; P. prlncipoides Emmons, and P. tenuicostatus Mighels, auctorum. 



This species was not actually obtained by the " Blake," but it was found 

 with many of the Blake species off the Carolina coast by the U. S. Fish Com- 

 mission. It was thought well to note here that this species by the character 

 of the foot and of the young shell forms a very complete link between Amu- 

 sium and such Pectens as P. caurinus, etc. It has precisely the foot of typical 

 Amusinm. 



Pecten caurinus Gould. 



Peclen caurinus Gould, Moll. U. S. Expl. Exp., Proc. Best. See. Nat. Hist., III. 



p. 345, Dec. 1850. 



Plato V. Fig. 4. 



The study of the group of Pectens included in Amusium and Pseudamusium 

 was made to utilize all available material, and in several cases resulted in the 

 identification of small specimens, supposed at first to be distinct, with the young 

 of forms which as adult would be classified in other sections of the genus 

 Pecten. Among these immature shells was the young of P. caurinus, which has 

 a striking resemblance to some species of Pseudamusium. It is figured here- 

 with as a matter of interest to those engaged in a study of the development 

 of the group. The specimen was dredged at Sitka, Alaska, in 1865. This spe- 

 cies grows to a large size and is found on both sides of the North Pacific. It 

 has no internal lirag, ami is not externally like Amusium, but in the charac- 

 ter of the foot it stands midway between the sucker-footed and the typical 

 Pectens. The foot is cylindrical, with the usual groove behind ; the tip is very 

 slightly enlarged, glandiform, with a small incision behind, which does not 

 look as if it could perform the office of a sucker with much efficiency. 

 The mantle margin is broad and thick ; set, in both valves, with a profusion 

 of well-developed ocelli and tentacular processes. The lips are arborescent at 

 their outer margin and radiately finely wrinkled inwardly. 



Pecten nucleus Born. 

 Pecten nucleus Born, Test. Mas., pi. vii. f. 2, 1780. 



Valves of this very neat little Pecten were found in 80-127 fms., off" Havana, 

 by Sigsbee. 



The validity of this species cannot be considered settled. A dwarf form of 

 P. dislocatus from southern waters seems to lead up to it by imperceptible 

 gradations. The name of Born is of course prior to that of Say, but it is said 

 that there are even earlier names. A larger supply of P. nucleus is needed 

 before the identification can be considered conclusive, and so for the present 

 I leave the names imdisturbed. 



