PHTLLOPODA 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 chitinous plates, like watch crystals, whose edges 

 fit together, one, two, or more eggs being in a single ephippium: about 

 8 families and several hundred species, most of which live in fresh water. 

 Key to the families of Cladocera here described : 



G! Carapace enclosing the entire body. 



6j One branch of second antennae with 2 segments, the other with 3.1. SIDIDAE 

 6 a One branch Of second Antennae with 3 segments, the other with 4. 



Ci First antennae minute 2. DAPHNIDAE 



c a First antennae long and beak-like 3. BOSMINIDAE 



6 3 Both branches of second antenna with 3 segments 4. LYNCEIDAE 



Oz Carapace not enclosing the legs and the abdomen. 

 6j Abdomen curved and rudimentary ; 4 pairs of legs ; fresh and salt 



water 5. POLYPHEMIDAE 



6 2 Abdomen straight and very large ; 6 pairs of legs 6. LEPTODOBIDAE 



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, with 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 



a a Dorsal branch of second antennae two-jointed. 



6 X First joint of second antennae with a long side branch 2. LATONA 



6 8 No such side branch 3. DAPHNELLA 



1. SIDA Straus-Diirkheim. Ventral branch of 

 second antennae with 2 segments; dorsal branch 

 with 3 segments; beak distinct: several species. 



S. crystallina (0. F. Muller) (Fig. 514). Shell 

 elongate with rounded ends; first antennae in male 

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



.,, r T -, i , tallina (Siissw. F. 



with brown, red, and blue spots; length 2 mm.: in Deut.). i, second an- 



i i i n, -11 T j -I tenna ; 2, first anten- 



clear lakes; often widely distnbuted; often com- na; 3, abdomen; 4, 



mon; Europe. 



2. LATONA Straus-Diirkheim. Ventral branch of second antennae 

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

 a long side branch: 1 species. 



