Chapter XXVII: Section I: Club of antennæ distinctly segmented only on the hind

side.

_Key to Genera._

_a._ No comb on head and thorax.

_a^1._ The internal incrassation, which extends from
the insertion of the mid coxa into the thorax,
joins the anterior edge of the mesosternite _Pulex_.

_b^1._ This incrassation joins the upper edge of
the mesosternite _Xenopsylla_.

_b._ With a comb on the pronotum only _Hoplopsyllus_.

_c._ With a comb on the pronotum and at the lower
edge of the head _Ctenocephalus_.