THE FAMILY OF NAIADES. XV11 



In vol. iii. of the Trans. Am. Phil. Soc, p. 398, Mr. Nicklin expresses the opinion 

 "that the seven genera, now referred to the family of Naiades, are founded in artificial dis- 

 tinctions, and not in nature; and that, in fact, the family contains but one genus." 



In consequence of the enormous extent to which the Family Naiades is expanded, it 

 is absolutely necessary to establish many groups and sub-groups, so as to make a systematic 

 arrangement accessible to the student of this branch of zoology. I therefore divide the 

 family into two genera, Margaron 1 and Plafiris. The first is divided into seven subgenera, 

 and the latter into three subgenera. These subgenera are again divided into symphynote 

 and non-symphynote, which are again divided into plicate, nodulous, spinous, and smooth 

 shells. These are subdivided into nine groups dependent on the outline of the plane of 

 the valve, viz., into quadrate, triangular, oblique, oval, oblong, subrotund, wide, obovate, 

 and arcuate, as in the following table : — 



1 In the previous edition, I proposed the name of Margarita, but, this name being pre-occupied by Dr. Leach 

 for a genus separated from Turbo, I now substitute that of Margaron (juafya^oc, TJnio). 



