PHYLLOPODA 333 



with the two branches (exopodite and endopodite) prominent, and used 



for swimming; abdomen small and usually bent under the thorax; 2 



large compound eyes which in many species unite to form a single 



median eye; a large dorsal brood sac in the female in which the eggs 



develop, the young animals being born with the form of the parent; 



the winter eggs are often provided with an extra shell called the ephip- 



pium, consisting of 2 chitinons plates, like watch crystals, whose edges 



fit together, one, tw^o, or more eggs being in a single ephippium: about 



8 families and several hundred species, most of w^iich live in fresh water. 



Key to the families of Cladocera here described : 



Ci Carapace enclosing the entire body. 

 6i One branch of second antennae with 2 segments, the other with 3.1. Sididae 



62 One branch of second antennae with 3 segments, the other with 4. 



Ci First antennae minute 2. Daphnidae 



Cg First antennae long and beak-like 3. Bosminidae 



63 Both branches of second antenna with 3 segments 4. Lynceidae 



©2 Carapace not enclosing the legs and the abdomen. 



61 Aldomen curved and rudimentary ; 4 pairs of legs ; fresh and salt 



water 5. Polyphemidae 



62 Abdomen straight and very large ; 6 pairs of legs 6. Leptodoridae 



Family 1. SIDIDAE. 



Head large and separated from the body by a depression and usually 

 with a beak; first antennae one-jointed^ but long in the male, wdth a 

 long terminal flagellum; second antennae very long, the two branches 

 having 2 and 3 segments respectively; 6 pairs of legs; heart elongate 

 and intestine straight, without liver sacs: several genera. 



Key to the genera of Sididae here described : 



«! Dorsal branch of second antennae three-jointed 1. Sida 



a2 Dorsal branch of second antennae two-jointed. 



&i First joint of second antennae with a long side branch 2. Latona 



62 No such side branch 3. Daphnella 



1. SiDA Straus-Diirkheim. Ventral branch of v^ , ^_ V 



second antennae wdth 2 segments; dorsal branch 

 wdth 3 segments; beak distinct: several species. 



S. crystallina (0. F. Miiller) (Fig. 5l4). Shell 



elongate with romided ends; first antennae in male ^ ( 3 



long, short in females ; body colorless, sometimes Fig. 514 — Sida crys- 

 • ,11 J -, , , " , 1 ,, ^ • /ff^//n(/ (Siissw. F. 



w^itli brown, red, and blue spots; length 2 mm.: in Deut.). 1, second an- 



elear lakes; often widely distributed; often com- na ; ' 3, abdomen^ ^4^ 



E brood sac. 



urope. 



2. Latona Straus-Durkheim. Ventral branch of second antennae 

 with 3 segments, dorsal branch with 2 segments, the first segment having 

 a long side branch: 1 species. 



