52 [March, 



The student who desires to study the group under discussion 

 should have examples preserved both in alcohol and mounted in 

 Canada balsam for mici'oscopical investigations. Fleas preserved in 

 alcohol should be stored in small tubes and the preservative fluid 

 should consist of three parts of absolute alcohol, two of water and one 

 of glycerine, the measurements being by volume. The tubes should, 

 of course, be carefully labelled both inside and out with the name of 

 the host from which the fleas were taken and with full date and 

 locality. 



Specimens to be mounted as microscopic slides should not be 

 treated with caustic potash, an antiquated method which rarely gives 

 satisfactory results. They should be cleared in oil of cloves and then 

 mounted in Canada balsam, as a rule without any more pressure than 

 that of the cover slip. Specimens which are much contracted and 

 therefore difficult to identify should be treated with peroxide of 

 hydrogen (H2O2) in which fluid they expand. 



Key to the Genera of British Fleas. 



1. Head with two ventral flaps anteriorly on each side 



(figs. 93, 94) 12 



. Head without these flaps, but often with genal comb of 



strongly chitiuized spines (figs. 1 — 7, 13, 57, 62, &c.) ... 2 



2. Abdomen without apical spines on any segment 3 



Abdomen with apical spines on some of the tergites 6 



3. No pronotal comb 4 



With pronotal comb 5 



4. No vertical internal rod in mesosternite (fig. 2) Pulex 



With vertical internal rod, f rons with tubercle (fig. 7) . . . 



Ornithopsylla 

 With vertical internal rod, frons without tubercle (fig. 1)... 



Xenopsylla 



5. Frons strongly angulate (fig. 6) Spilopsyllus 



Frons not angulate, without tubercle, 2 or 1 genal spine 



(fig. 3) ArchaeopsyUa 



Frons not angulate, 8 (rarely 7) genal spines (figs. 4, 5) 



. . . Ctenoceplialus 



6. Eye well developed, no genal comb (fig. 13) Ceratophyllus 



Eye somewhat reduced or absent, genal comb present (figs. 



57,62). 



