e. Labial palpi four or five-segmented; symmetrical; hind coxæ with patch of spines inside; row of six spatulate spines on each side in front of the antennæ. _C. ornate_ found on a California mole. _Corypsylla_ ee. Labial palpi two-segmented, transparent, membranous. On hares. _Spilopsyllus_ Baker dd. No ctenidium on the head. e. Pronotum with ctenidium. DOLICHOPSYLLIDÆ f. Labial palpi five-segmented, symmetrical. g. Antepygidial bristles one to three; eyes present. h. Inner side of hind coxæ distally with a comb of minute teeth; falx present. On rodents and carnivores. _Odontopsyllus_ Baker 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. e. Head rounded in front (fig. 92a). Dog flea. C. CANIS ee. Head long and flat (fig. 92b). Cat flea. C. FELIS dd. Neither head nor pronotum with ctenidium. Labial palpi asymmetrical, membranous behind. PULICIDÆ e. Mesosternite narrow, without internal rod-like thickening from the insertion of the coxæ upwards. Human flea, etc. PULEX L. ee. Mesosternite broad with a rod-like internal thickening from the insertion of the coxæ upwards (fig. 89). X. (LŒMOPSYLLA) CHEOPIS, plague or rat flea. XENOPSYLLA