FAMILIES OF CLADOCERA 53 



Fam. 4. Bosminidae : feet equidistant, five or six pairs ; the first 

 antennae of the female immobile, with eense-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. 



B. Both rami of second antenna three-jointed. 



Fam. 6. Lynceidae 1 : five or six equidistant pairs of thoracic feet. 

 Intestine coiled. 



i. Six pairs of thoracic limbs. Head and thorax separated by a 

 deep depression. Intestine with one caecum, stomach with 

 two. Female carries many summer - eggs. Eurycercus, 

 Baird. 



ii. Five pairs of thoracic limbs. Head and thorax separated by a 

 slight groove or not at all. Anterior digestive caeca absent. 

 Female carries only one or two summer-eggs. 

 A. Body elongate, oval. 



a. Head carinate, the eye far from the anterior cephalic margin. 

 Camptocercus, Baird : body laterally compressed. Second 

 antennae with seven swimming hairs. Telson more than half 

 as long as the shell. Acroperus, Baird (Fig. 23) : body 

 compressed. Second antennae with eight swimming hairs, of 

 which one is very small. Telson less than half as long as 

 the shell. 



b. Head not carinate, the eye near the anterior cephalic margin. 

 Alonopsis, Sars : terminal claws of telson with three accessory 

 teeth. Alona, Baird : terminal claws of telson with one 

 accessory tooth (includes sub-genera Leydigia, Alona, Harpo- 

 rhynchus, Graptoleberis). Peracantlia, Baird (Fig. 14) : terminal 



1 More properly Chydoridae,but the universally known name Lynceidae is con- 

 venient. 



