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.