4 MOSQUITOES OF NORTH AMEEICA 



These characters are, we think, easily appreciable by anyone familiar with the 

 names of the parts of the mosquito, and no especial difficulty should be met with 

 in determining specimens of Sabethini that are in good condition, for the specific 

 characters of this group seem well fixed and not subject to much individual 

 variation. 



In separating the genera of the Culicini, we have been obliged to resort to 

 special characters for nearly every genus, as they do not divide into large groups 

 of genera on single characters. The Culicini are in a plastic condition, the 

 several forms constituting a more or less continuous series from the lowest to 

 the highest. This is especially shown in the members of the highest genera, 

 particularly the large genus Culex, where the species are very closely allied and 

 subject to considerable individual variation. We use, in generic definition, the 

 scutellum, whether distinctly trilobed or not ; the mesothorax, whether specially 

 elongated or roundedly elliptical ; certain differences in venation ; the elongation 

 of the second antenna] joint; the approximation of the enlarged prothoracic 

 lobes in one genus ; the peculiar shortening of the fourth joint of the fore tarsus 

 in another ; finally we come to a group of five genera which we have divided on 

 the modification of the hind tibial scraper. This structure is visible only when 

 the legs have been prepared and mounted in balsam, but we find it a good char- 

 acter of last resort. 



The five genera in question are Psorophora, Aedes, Mansonia, Culex and 

 Carrollia. PsoropJiora and Aedes, in the female, can be distinguished at a 

 glance from the others by the shape of the abdomen, which is pointed, with 

 prominent cerci, and in nearly all cases this will suffice, as specimens are gen- 

 erally of the female sex. The small genus Carrollia can be distinguished from 

 Culex by the compressed abdomen. The Mansonia are generally recognizable 

 by their specific characters, but in cases of doubt recourse should be had to the 

 tibial scraper, which can be seen by mounting one hind leg for the microscope. 



Lutzia is closely allied to Culex, but we separate it by the unusually large 

 empodia between the tarsal claws. This is no doubt an adaptive character of no 

 fundamental importance, but serves to separate these large species. To separate 

 Psorophora, Aedes and Mansonia, we have been obliged to use different char- 

 acters for the two sexes, which is the only case in which we have been forced to 

 this undesirable course. It has seemed impossible to unite the last two genera 

 on account of the peculiar larval structures of Mansonia, as well as the structure 

 of the female adult, correlated with its habit of depositing the eggs in boat-like 

 masses. 



We have separated the species of Deinocerites by the structure of the cerci 

 of the female, which can only be well seen in balsam mounts. The antennae of 

 the male serve in part to separate specimens of that sex, but in doubtful cases, 

 with only males at hand, the geographical distribution will have to be considered 

 in arriving at a determination. 



In Culex we have used the coloration and markings of all the parts. The 

 genus contains two distinct groups, Culex proper and the peculiar group inhabit- 

 ing the water in the leaves of bromeliaceous olants, Microculex Theobald. These 



