THE CANADIAN ENTOMOLOGIST. 



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authors), Naucoridce (including Nerthridce., which has been joined to this 

 family), and Belostomatidie. Here we have a series which, while the 

 families are distinct, is nevertheless a direct one, in which the divergence 

 between genera is not unbridgable. The two remaining families are 

 obviously highly specialized, and differ as much between themselves as 

 they do from the other four. On the other hand, I believe his arrange- 

 ment of the Nepoidece is susceptible of advantageous modification. It 

 appears to me evident that the Hydro met r idee and Mesoveliidce are not 

 subfamilies of the Gerridce, but are entitled to family rank. The true 

 Gerridce are much older than either and spring from the main stem shortly 

 after the Nepidce, while the Hydrometridce are more closely allied to the 

 Reduviidce proper, and the Mesoveliidce to the Nabidcz. In this respect 

 I think Kirkaldy's tree should be modified thus : 



o Nabid.^e 



Mesoveliidce o- 



Gerrid^: o- 



o Reduviid.*: 



■° HVDROMETRID.'E 



-° Enicocephalid.*: 



■° Nepidce 



The Gerrida. are thoroughly and completely adapted for their semi- 

 aquatic life ; the Hydrometridce are in process of adaptation, and the 



