ORDER SIPHONAPTERA (APHANIPTERA) : FLEAS 195 



["Club of antenna incompletely segmented ; only one antepygidial 

 bristle on each side = Hoplopsyllus. 



I Club of antenna completely segmented ; more than one ante- 

 pygidial bristle on each side = Ceratophyllus. 



("None of the abdominal terga with combs = 7. 



-] One or more of the abdominal terga with a comb 



I = Hystricopsylla. 



f Bristles of hind border of tibise not in a close-set row = 8. 



\ Bristles of hind border of tibiae in a close-set row =CtenopsyUa. 



[Last tarsal segment of first and second legs with five lateral bristles 

 on either side, of third legs with four = Neopsylla. 



I Last tarsal segment of first and second legs with four lateral 

 bristles, of third legs with three = Ctenophthalmus. 



Genus Pulex, L. (Fig. 76). In this genus there are no 

 combs on head and pronotum, the eyes are large, and there 



Fig. 76. — Common Flea {PuUx irritans). 



is only one pair of antepygidial bristles. The best known 

 species is the human flea, P. irritans, L., which is as cosmo- 

 politan as its host, and also attacks other animals, including 

 the rat. Its principal specific characters are as follows : — 

 there is no transverse row of bristles on the head, each 

 abdominal tergum has only one belt of bristles, the labial 

 palps are long and are composed of 3 segments, and there are 

 numerous teeth in an irregular row on the inner side of the 

 hind coxa. 



Genus Xenopsylla, Glink. (Fig. 'jj'). This genus differs 

 very slightly from Pulex, the chief distinction being the 

 presence of an internal chitinous thickening that runs from 

 the coxal articulation of the second leg upwards through the 



