Summary of Characters of the British Genera.[[34]]
Tribe I. Calyptomera, Sars.—The post-cephalic portion of the body enveloped in a free fold or carapace.
A. Six pairs of thoracic feet, the first pair not prehensile (Ctenopoda).
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.
Fig. [19].—Daphnia obtusa, male, × about 50. Oxford. A.1, First antenna; Th.1, first thoracic appendage.