LETDIG OX DAPHNIID.B. 31 



or slightly yellow ; in some few cases, even with a bluish or greenish tint. 

 The blood-cells are generally colourless, and their number varies accord- 

 ing to the richness or poverty of food. In some species, however, as, for 

 instance, in Polyphemus o cuius, the blood-cells appeared to be very few 

 in number, or even almost entirely absent. 



I subjoin a list of the genera proposed by Prof. Ley dig, with their 

 principal characters : — 



SIDA. 



Six pairs of legs. The large antennae with two branches, one of 

 them two-jointed; the other three- jointed. 



HOLOPEDITJM. 



Characters of Sida. The large antennas not branched. 



LATONA. 



Characters of Sida. The large antennas with three branches. 



DAP IOTA. 



Five pairs of legs. The large antennas with two branches ; one 

 three-jointed, the other four-jointed. 



MACROTHEIX. 



Legs and general characters as in Daphnia. The plumose hair of 

 the first segment of the three-jointed branch of the large antennas is the 

 longest, and its second segment is toothed like a saw. 



ACANTHOCEBCUS. 



Characters generally as in Daphnia. The four-jointed branch of the 

 large antennas has only three plumose hairs ; the three-jointed branch 

 has five, the one belonging to the first segment being the longest. 



PASITHEA. 



Characters generally as in Daphnia. Both branches of the large an- 

 tennas have five setas. Post- abdomen peculiar; the part lying before the 

 anus small, the posterior portion elongated. 



BOSMIXA. 



Five pairs of legs. Large antennas two-branched ; the one branch 

 with four segments, and three bristles ; the other with three segments, 

 and five bristles. The head is produced in front into two long horns. 



LYNCETTS. 



Five pairs of legs. Stem of the large antennas short, with two 

 three-jointed branches. Accessory eye large. 



