REVISION OF THE SARCOPSYLLIDAE 33 
exhibited least in Echidnophaga. In this genus, judging from our material, the seg- 
mental plates of the pregnant are but little separated, the plates covering each 
other at least partly. The abdomen retains its general shape, the enlargement being 
in some or the species described below hardly equal to that found in Pulex hritans. 
The female abdomen of Hectopsylla is quite different. The segmental plates are 
here placed widely apart when the abdomen is distended, the dorsal plates being quite 
separate from the ventral ones, the abdomen resembling in this respect that of the 
genera Chaetopsylla, Malacopsylla, and Vermipsylla. In the genus Hectopsylla, however, 
there is one very singular specialization, restricted to this genus, not being met with 
anywhere else among Siphonaptera as tar as we know. The sternit.es or segments 
two to seven, which in other Siphonaptera consist each of a single plate, are in 
Hectopsylla completely divided in the middle line so that these segments bear three 
plates instead of two, all well apart from one another on the extended abdomen. This 
division of the ventral plate of the segments minimises the resistance of the plates. 
The swollen abdomen of a $ Hectopsylla has consequently quite a different aspect from 
that of a $ Echidnophaga, the connecting membranes being well exposed and the three 
brown plates of each segment (two to seven) being easily recognized on the white 
background. . We mention incidentally that the abdominal sternites of the of 
Hectopsylla are not divided. 
The swollen abdomen of Dermatophilus is again quite different from that of any 
other Siphonapteron. In this genus the abdomen becomes globular by swelling enor- 
mously in the central region. The three proximal segments are pushed forward, as 
Fig. D 
it were, and the other segments backwards, the membrane between the third and fourth 
segments being enlarged to a very great extent. In D. caecata the abdomen totally 
envelops the head and thorax as shewn in the accompanying diagram (Fig D). 
Owing to the great diversity in the development of the legs of the Sarco- 
PsyUiaae, both as regards the degree of specialization as well as the direction of 
F 
