March, 1015.] 49 



A SYNOPSIS OP THE BRITISH SIP HON APTERA. 

 BV THE HON. X. CllAKl-ES ROTHSCHILD, M.A., F.L.«., Pii.E.S. 



Plates VII— XIV. 



The Siplionaptera, or fleas, form a group of insects apparently 

 not very closely related to any of the other orders of Hexapoda. The 

 group is being more and more studied by entomologists here in 

 England, and no publication exists for the ready identification of the 

 British species. To supply this want the author has written the 

 present article. Its object is explained by the title, i.e., to furnish a 

 key, or ready means of identification of all the fleas so far recorded 

 from the British Isles. The descriptions must not be regarded as full 

 descriptions, but as merely a selection of those characters which afford 

 an easy diagnosis of the various species. 



Fleas are parasitic on mammals and birds, and the chief hosts of 

 each species are given in this treatise, but it should be remembered 

 that frequently a number of quite different animals harbour the same 

 species of flea, and that predaceous animals often acquire, and 

 apparently retain for some time, the fleas of their prey. 



The classification and diagnoses given in the present article are 

 as a rule valid for the British genera and species only. A general 

 classification of the whole group based on all the known genera and 

 species has not yet been satisfactorily attempted. The main division 

 of the group, however, employed in the present article, into Fracticipita 

 and Infegricipita (Oudemans)* is a classification which seems to reflect 

 the real phylogenetic relations of all the known genera. 



The student who desires to identify a species should first examine 

 the key to the genera and on deciding to which genus the insect in 

 question belongs, he should confirm the identification by carefully 

 comparing it with the diagnoses of the genera. When the genus has 

 been determined with certainty the keys and diagnoses of the species 

 should then be consulted. Before any of the keys or diagnoses can be 

 used to advantage the student must familiarise himself with certain 

 details of the chitinised external skeleton of the flea which are made 

 use of in this article, 



Antennal groove. The groove in the centre of the head in which 

 the antenna lies when at rest, and which divides the head into an 

 anterior (= f rons) and a posterior (= occiput) portion (cf,.pl. V^f).-- 



.-^.v . ^ or c Q/vg 



* Cf. Novltates Zoologicac, vol. xvl, pp. 133-158 (190<)>; ^^V^ Oj> 



l' ^ MARIS 1915 ^ 



