Adapted from a table published by Oudemans.
a. Elongated fleas, with jointed (articulated) head, with combs (ctenidia) on head and thorax; with long, oval, free-jointed flagellum of the antenna ([fig. 92d]). Suborder FRACTICIPATA
b. With ctenidia in front of the antennæ and on the genæ (cheeks); maxillæ with acute apices; labial palpi five-segmented, symmetrical; eyes poorly developed or wanting. On rodents. Hystrichopsyllidæ
c. Abdominal segments without ctenidia.
d. Post-tibial spines in pairs and not in a very close set row; head with ctenidia. Ctenophthalmus Kol.
dd. Post-tibial spines mostly single and in a close set row. Ctenopsyllus and Leptopsyllus. The last genus has recently been erected for L. musculi, a widely distributed species occurring on rats and mice.
cc. Abdominal segments with one or more ctenidia; post-tibial spines in numerous, short, close-set transverse rows on posterior border with about four spines in each row. H. americana. Hystrichopsylla Taschenb.
bb. With only two pairs of subfrontal ctenidia; labial palpi five-segmented, symmetrical; eyes vestigial or wanting. On bats. (= Ischnopsyllidæ). Nycteridipsyllidæ
With more or less blunt maxilla; all tibiæ with notch; a single antepygidial bristle; metepimeron without ctenidium. N. crosbyi from Missouri was found on bats. Rothschild suggests that this is probably the same as N. insignis. (= Ischnopsyllus = Ceratopsyllus), Nycteridiphilus
aa. Head not jointed, i.e. the segments coalescent, traces of the segmentation still being visible in the presence of the vertex tubercle, the falx (sickle-shaped process), and a suture. Suborder INTEGRICIPITA