hh. Inner side of hind coxæ without comb or teeth. Many North American species on rodents. Ceratophyllus Curtis
gg. Antepygidial bristles five on each side; eyes absent; suture white. D. stylosus on rodents. Dolichopsyllus Baker
ff. Labial palpi four or five-segmented; asymmetrical (membranous behind), apex acute. Hoplopsyllus anomalus found on Spermophiles in Colorado. Hoplopsyllidæ
ee. Pronotum without ctenidium. Anomiopsyllus californicus and nudatus on rodents. Anomiopsyllidæ
cc. Very short fleas; flagellum of the antenna with pseudo-segments coalescent; thorax much shorter than the head and than the first tergite Hectopsyllidæ
Flagellum of the antenna with six coalescent pseudo-segments; maxilla blunt. The chigger on man ([fig. 93]). D. penetrans. (= Rhynchoprion = Sarcopsylla) Dermatophilus Guérin
bb. Flagellum short, round, free portion of the first segment shaped like a mandolin.
c. Thorax not shorter than the head, longer than the first tergite; flagellum either with free segments or in part with the segments coalescent.
d. Head and pronotum with ctenidium; labial palpi asymmetrical. Archæopsyllidæ
With four subfrontal, four genal, and one angular ctenidia. Widely distributed. Ctenocephalus Kol.