NATURAL HISTORY OF THE BAY SCALLOP 
571 
studied the circulatory system by means of injections (Garner, 1838-39, 1841) and 
attributed the great size of the adductor muscle to its use in clapping the shell in the 
swimming process. He suggested the importance of the gills for classification and 
discovered (see Kellogg, 1892) that the sexual products are discharged through the 
kidney. 
Modern studies which have been especially useful are the account of the scallop 
fishery by Ingersoli (1887) in The Fishery Industries of the United States; papers by 
Jackson (1890) and Kellogg (1892 et. seq.); the Memoirs by Drew (1906) and Dakin 
(1909); and the account by Belding (1910). 
CLASSIFICATION AND RELATIONSHIP 
Among the schemes of classification of lainellibranchs, that employing the struc- 
ture of the gills is the simplest and seems to be gaining most favor among students 
of recent forms. The possibility of such a scheme was suggested by Lankester in 1883. 
Development is due to various workers, notably Pelseneer, Menegaux, and Ridewood. 
Pelseneer’s classification of orders (1906) is essentially that of Ridewood (1903); 
but with certain order names previously given by Pelseneer used instead of the new 
names proposed by Ridewood, and with the Septibranchs retained as an order. Under 
this scheme forms with flat, platelike, unreflected gill filaments (Protobranchia) are 
regarded as most primitive; those with reflected filaments held together in lamellae 
by interlocking cilia (Filibranchia) as higher in advancement; those with reflected 
filaments joined one with the other by vascular connection (Eulamellibranchia) as 
having attained the highest development; and the Septibranchs as being forms with 
degenerate gills. 
In such a classification the scallops belong with the Filibranchia but evidently 
are close to the Eulamellibranchia, because vascular filamentary connections are 
found in the giant or sea scallop ( Pecten tenuicostatus Mighels, as employed by Drew 
but, according to Dr. Paul Bartsch, in correspondence, Pecten grandis Solander). 
Cooke (1895) and also Parker and Haswell (1897) employ a somewhat different 
classification with an intermediate order, the Pseudolemellibranchiata, in which are 
placed the oysters and the scallops with a few others. Although, as previously 
noted, the intermediate position for the scallop is indicated, the oysters would seem 
clearly to belong with the Eulamellibranchiata, and it may be questioned whether 
this intermediate order does not increase rather than decrease the difficulties. 
In its main outline, classification according to the gill structure has the advantage 
of being a simple, logical, readily understandable one, which presents a reasonable 
interpretation of phylogenetic relationship. It seems the most useful scheme devel- 
oped. Undoubtedly the understandable logic of the main outline of classification 
according to gill structure has had much to do with its favorable reception and may 
have unduly influenced zoologists. In the classification which Dali (1895) introduced 
after many years of study, the attempt is made to take into consideration all struc- 
tural evidence. In this classification Pectinacea is constituted quite differently and 
placed with groups including Solenomya, Ostrea, and others in the order Teleodes- 
macea. The class is termed Pelecypoda. See also Rice (1900, 1908) and Verrill 
(1899). 
The bay scallop almost universally is placed in the genus Pecten, but as to the 
species there is some difference of opinion and usage. Dali (1898) placed w’hat I term 
the bay scallop — ranging from Massachusetts to the Gulf of Mexico and even to 
Brazil — in one species. Davenport (1903), largely as a result of “ray counts,” finds 
