THE FLEAS OF NORTH AMERICA 6 



or host distribution. However, if there is a break in the variation 

 of these characters, they are considered of subspecific importance re- 

 gardless of whether the differences are correlated with geographical 

 or host distribution. A subspecific character is considered as usually 

 being morphologically more distinctive than a varietal character, 

 and by that token a subspecies is regarded as taxonomically of more 

 importance than a variety, although from the nomenclatorial point of 

 view the two are treated alike. 



Characters used for specific purposes less frequently refer to colora- 

 tion, or length of setae, or even size. They are regarded as essentially 

 the same as those used for the subspecies, except that they are more 

 obvious, less variable, or have a greater morphological significance. 

 Characters resulting from hybridization or local environmental in- 

 fluences are not here considered as good specific characters. 



In preparing this taxonomic review an attempt has been made 

 to follow a conservative policy in the treatment of the different cate- 

 gories, avoiding alike the extremes of the "splitter" and those of 

 the "lumper." It is the writers' opinion that in the Siphonaptera the 

 tendency has been toward too much "splitting." This is strikingly 

 shown by the manner in which the genus Ceratophyllus Curtis has 

 been split up in recent years. On this Jordan (43, p. 70) has com- 

 mented as follows : 



* * * The splitting-up of Ceratophyllus has begun, and there is no means of 

 stopping the process of dissolution from going on. * * * If I here inflict on 

 science a number of new generic names, I plead the excuse that the divisions 

 of Ceratophyllus I here define would inevitably be named by somebody else, 

 probably by someone who does not know these fleas, as has happened in other 

 orders of animals. 



In regard to the splitting up of Ceratophyllus and certain other 

 genera the present authors have dealt rather firmly. Many of the 

 segregates are retained as subgenera, being in reality excellently 

 fitted for such a rank, while others are reduced to synonymy. 



In the part of this publication dealing with the taxonomy of 

 species, subspecies, and varieties the paragraph headings "Cotype 

 Hosts" and "Cotype Localities" have been introduced in those in- 

 stances in which cotype material came from more than one host and 

 more than one locality. 



The number of described genera and species of North American 

 fleas has increased very rapidly in recent years. In this paper 61 

 genera, 14 subgenera, 209 species, and 63 subspecies and varieties of 

 fleas are listed from North America and the West Indies. 



THE ECONOMIC IMPORTANCE OF FLEAS 



Fleas are of economic importance in two ways. First, by their 

 direct attacks on man and his domestic animals they cause irritation, 

 loss of blood, and in severe cases the loss of life. Second, because 

 of their blood-sucking habits they are important transmitters of 

 certain internal parasites and disease-producing organisms. 



Fleas are probably best known as household pests. Their presence 

 in houses, under certain conditions, may cause the occupants great 

 annoyance. Their occurrence there is due to the presence of their 

 natural hosts, either in the houses or in nearby quarters. These are 



