REVISION OF THE SARCOPSYLLIDAE 35 
The trochanters of the Siphonaptera bear anteriorly a pair of bristles on or 
near the middle. These bristles are present in the Sarcopsyllidae, but have a more 
distal position than in other fleas. In Hectopsylla the groove in which these bristles 
are inserted on the posterior trochanter is enlarged and deepened, appearing as an 
excision in side-view ; the upper edge of this groove projecting forward and down- 
wards (PI. I, Fig. 6). In a similar wav, the pair of subbasal ventral bristles of the 
hind femur is situated in Hectopsylla in a deep groove, the portion of the femur in 
front of this groove forming a prominent hook (PI. I, Fig. 6). Behind the groove 
the ventral edge of the femur is angulate, the angle corresponding to the small tooth 
found in several species of Pulex from the Old World (for instance, Pulex cleopatrae, 
pallidus, etc.) Those subbasal ventral bristles of the hind femur are preserved in 
Hectopsylla and Echidnophaga, but they are absent from Dermatophilus. The place 
where they are situated in those genera is also in Dermatophllus less chitinized than 
the rest of the femur. 
The skeleton of all the femora is in Echidnophaga, and to a less degree also in 
Dermatophllus, internally incrassate just behind the subbasal membranaceous place, as 
is also the case in Pulex. ^s in many Pulicidae there is on the inner surface* of the 
hind femur of the Sarcopsyllidae a row of bristles. The number of bristles in this row 
is very much reduced in some species of Echidnophaga, there being only two or three 
bristles left in Echidnophaga aethiops. The hairs at the dorsal edge of the mid and 
hind femora vary much in number. The curved apical dorsal bristle of the femora 
is stout in Echidnophaga, but short and very weak in Dermatophilus, the species of the 
genus Hectopsylla being in this respect intermediate. 
We have stated above that the tibiae are practically devoid of external bristles in 
all the species of Sarcopsyllidae, the row accompanying the dorsal bristles in other 
Siphonaptera being represented by one or two bristles only, or not at all. The dorsal 
bristles, however, do not present such a uniform development in the various species. 
We regard as the most generalized state of development in Siphonaptera a tibia with 
eight pairs of dorsal bristles placed in notches, including the apical bristles. One or 
the other of these pairs is usually reduced, the notch being obliterated or vestigial. 
The fifth pair and the apical pair are the most prominent, the third and the sixth are 
the first to be reduced or to disappear altogether, and after these the seventh pair. 
The same order is followed in the Sarcopsyllidae. In this family there are from three 
to seven pairs of dorsal bristles on the mid tibia, the lowest number being found in 
Dermatophilus. The proximal pair is always small, and the notch in which it is situated 
is practically obliterated ; it is altogether lost in Dermatophilus, which retains the 
second, fifth, and the apical pairs. The notch of the third pair is also never developed 
in the Sarcopsyllidae, and the pair of bristles is, at the utmost, represented by a short 
but stout sublateral bristle and a minute hair. 
* These bristles have been figured, by all authors we believe, as standing on the outer side (if the femur. 
