Fig. [22].—Bosmina sp., female, × about 80. Lake Constance.
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.
a. The four-jointed ramus of the second antenna with four swimming hairs. Macrothrix, Baird: the first antennae of the female flattened, curved. The intestine simple, straight. Streblocerus, Sars: first antennae of the female very little flattened, curved backwards and outwards. The intestine coiled, the stomach with two forwardly-directed caeca.
b. The four-jointed ramus of the second antenna with only three swimming hairs. Drepanothrix, Sars.
iii. Six pairs of thoracic limbs; the labrum provided with an appendage. Acantholeberis, Lilljeborg: appendage of labrum long, pointed, and setose. Intestine without caecum. Ilyocryptus, Sars: appendage of the labrum short, truncated. Intestine with a caecum.