Streptocephalus, Baird—Second antennae of ♂ 3–jointed, the last joint bifid; an external filamentous appendage. S. torvicornis, Wagn., Poland.
Chirocephalus, Prévost—Second antennae of ♂ 3–jointed, with a jointed internal appendage, which bears secondary processes, four cylindrical and one lamellar. C. diaphanus, Prévost (Fig. [2], p. 20).—Britain, Central Europe.
b. Abdominal segments five or fewer, and a telson. Anal lobes small or 0, sparsely or not at all setose.
Artemia, Leach—Second antennae of ♂ without filamentous appendage, 2–jointed, the second joint lamellar. A. salina, Linn.—Brine pools of the Palaearctic region.
c. Hinder abdominal segments united with telson to form a fin; anal lobes absent.
Thamnocephalus, Packard—Head with a branched median process of unknown nature. Only species T. platyurus, Packard—Kansas, U.S.A.
B. Nineteen pairs of praegenital ambulatory limbs.
Polyartemia, Fischer—Second antennae of ♂ forcipate; ovisac of ♀ very short. Only species P. forcipata, Fisch.
Fam. 2. Apodidae.[[28]]—Carapace well developed as a depressed shield, covering at least half the body. Eyes sessile, covered; no male clasping organs; anal lobes long, jointed cirri.
Apus, Scopoli—Telson not produced backwards over the anus; endites of first thoracic limb very long. A. cancriformis, Schaeffer—Britain, Europe, Algiers, Tunis. A. australiensis, Central Australia.