=Fam. 1. Sididae=: second antennae biramous in both sexes. _Sida_, Straus (Fig. 11): second antenna with three joints in the dorsal ramus, two in the ventral; the rostrum large, the teeth on the telson many. _Latona_, Straus: second antenna with two joints in the dorsal ramus, three in the ventral, the proximal joint of the dorsal ramus provided with a setose appendage. _Daphnella_, Baird: second antenna with the joints as in _Latona_, but with no setose appendage. =Fam. 2. Holopediidae=: second antennae not biramous in the female; a rudimentary second ramus in the male. _Holopedium_, Zaddach. B. Four to five or six pairs of thoracic feet, the anterior pair prehensile (ANOMOPODA). =A.= Ventral ramus of second antenna with three joints, the dorsal ramus with four. =Fam. 3. Daphniidae=: five pairs of thoracic feet, with a gap between the fourth and fifth pairs. The stomach with two forwardly-directed diverticula. [Illustration: FIG. 19.—_Daphnia obtusa_, male, × about 50. Oxford. _A._1, First antenna; _Th._1, first thoracic appendage. ] i. First antennae of female short. α A median dorsal spine on posterior margin of carapace. _Daphnia_, O. F. Müller (Fig. 19): first antennae of female not mobile. The head separated from the thorax only by a slight constriction or not at all. Cuticle with a quadrate rhomboid pattern. _Ceriodaphnia_, Dana: first antennae of female mobile. The head separated by a deep depression from the thorax. Cuticle with a polygonal pattern. β A pair of ventral spines on posterior margin of carapace. _Scapholeberis_, Schoedler (Fig. 20). [Illustration: FIG. 20.—_Scapholeberis mucronata_, female, × 25. Oxford. ] γ No spine on posterior margin of carapace. _Simocephalus_, Schoedler (Fig. 10, p. 39): the cuticle with a pattern of parallel branching ridges. [Illustration: FIG. 21.—_Moina rectirostris_, female, × 24. Oxford. ] ii. First antennae of female long, mobile. _Moina_, Baird (Figs. 16, 17, 21): median eye absent. Posterior margin of carapace without a spine. [Illustration: FIG. 22.—_Bosmina_ sp., female, × about 80. Lake Constance. ] [Illustration: FIG. 23.—_Acroperus leucocephalus_, × about 35. Oxford. ] =Fam. 4. Bosminidae=: feet equidistant, five or six pairs; the first antennae of the female immobile, with sense-hairs arranged in rings, not forming an apical tuft. The intestine uncoiled; no caeca. _Bosmina_, Baird (Fig. 22). =Fam. 5. Lyncodaphniidae=: four, five, or six pairs of equidistant thoracic limbs; the first two pairs prehensile. First antennae of female mobile, with apical sense-hairs. Intestine coiled or straight. i. Four pairs of thoracic limbs. _Lathonura_, Lilljeborg. ii. Five pairs of thoracic limbs.