_a._ Abdomen of six well-formed segments and a telson; anal lobes well formed, their margins setose. _Branchinecta_, Verrill—Second antennae of ♂ without lateral appendages; ovisac of ♀ elongated. _B. paludosa_, O. F. Müll.—Circumpolar. _Branchiopodopsis_, G. O. Sars[27]—Second antennae of ♂ as in _Branchinecta_; ovisac of ♀ short. _B. hodgsoni_, G. O. Sars—Cape of Good Hope. _Branchipus_, Schaeffer—Second antennae of ♂ with simple internal filamentous appendage. _B. stagnalis_, Linn.— Central Europe. _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. _Lepidurus_, Leach—Telson produced backwards to form a plate above the anus; endites of first thoracic limb short. _L. productus_, Bosc.—Central Europe. _L. viridis_, Southern Australia, New Zealand, _L. patagonicus_, Bergh, Argentines.