NO. 2063. NORTH AMERICAN PARASITIC C0PEP0D8— WILSON. 599 



the second division, and the structure of the attachment organs for 

 the third division. 



Since Gerstaecker there has been no serious attempt at a revision 

 of the classification of this family, though valuable suggestions have 

 been made by Neresheimer (1909) and others. 



The following scheme of classification is a combination of all these 

 which have preceded it, with such additions as more recent investi- 

 gations demand. The most important of these additions and the 

 one thing which can give the present scheme any credit, if indeed it 

 can claim such, is the use of the male. The males are less degenerate 

 than the females and the only reason why they have not hitherto 

 been employed by systematists has been the fact that so few of them 

 have been known. Neaily every investigator has called attention 

 to the desirability of the male as a basis of generic distinction. Some 

 have plainly stated that the ultimate decision in every question of 

 generic vahdity must rest with the male. This being appreciated 

 even by those who lacked the facts necessary to use it, it follows that 

 type distinctions among the males ought to possess superior value 

 in distinguishing the genera. Accordingly, so far as has been pos- 

 sible in the following classification, each genus presents a certain 

 type of male, which is fully described and figured in the genus diag- 

 nosis. To facilitate comparison these 17 male types are shown side 

 by side in plates 25 to 28, the scale mark by the side of each repre- 

 senting one-tenth of a millimeter. 



TABLE OF GENERA. 



1. Maxillipeds inside of second maxillae and the two close behind the mouth tube- 

 cephalothorax neither narrowed nor flattened, in line with the trunk or inclined 

 forward Lernaeopodinae, 2. 



1. Maxillipeds inside of second maxillae and the two removed a considerable dis- 

 tance behind the mouth tube; cephalothorax much narrowed and flattened, 

 inclined backward, or arched dorsally Tracheliastinae, 5. 



1. Maxillipeds removed some distance behind the mouth tube, second maxillae an 

 equal distance behind the maxillipeds; cephalothorax neither narrowed nor 

 flattened, in Une with the second maxillae and at right angles to the trunk 

 ^xis Brianellinae, 6. 



1. Maxillipeds close to the mouth tube, second maxillae removed a considerable 



distance behind them; cephalothorax narrowed and wormUke, in line with 

 the trunk axis or inclined backward Clavellinae 7. 



2. Second maxillae much longer than the cephalothorax; the latter always separated 



from the trunk by a well-defined groove and often by a sort of neck 3. 



2. Second maxillae stout and but little longer than the cephalothorax; the latter 



fused with the body, without any traces of separation or segmentation 4. 



3. No dorsal carapace on the cephalothorax; a genital process but no anal laminae, 



posterior processes, or abdomen; trunk stout and unsegmented. 



Salmincola, new genus, p. 603. 



3. A partial dorsal carapace; no anal laminae or posterior processes, but a distinct 



abdomen, sometimes segmented; trunk also often partially segmented; male 



type ^, pi. 25 Achtheres Nordmann, 1832, p. 617. 



