Relations of Bunops in the Family Macrothricidce. 335 
family, crested forms are found. These are Daphnia, especially 
Hyalodaphnia , in the Daphnidoe ; Acroperus and Camptocercus in 
the Lynceidce and Bu?iops in the Macrothricidce. These genera 
too, are much compressed laterally. In all these families, there 
are genera with a post-anal projection of the post-abdomen, and 
genera without such projection. Moina among the Daphnidoe 
has such a projection conspicuously developed, and Ophryoxus 
and especially Ilyocryptus among the Macrothricidce. In the 
Lynceidce, such a projection is the rule, to which Eurycercus is 
the only exception. No order in the animal kingdom offers bet¬ 
ter illustrations of convergence of development, than does the 
Cladocera. 
When we attempt to compare Bunops with other genera of 
the Macrothricidce , we are at once struck with the multiplicity 
and complexity of the relationships of these genera. While it 
is clear that Bunops is one of the most specialized members of 
the family, its relationships to less developed genera are by no 
means simple, as will appear from a study of its several parts. 
As has been already said, Bunops is the crested Macrotliricid , 
corresponding to Daphnia or Camptocercus in the other main 
families of the Cladocera. One difference between these crested 
forms of different families must be noted. In Daphnidoe and 
Lynceidce , the crest of the head is the most developed part of 
the keel; while in Bunops , the crest extends but a little way 
upon the head. Other genera of the Macrothricidce are keeled or 
slightly crested, though to a much less degree than Bunops. 
Drepanothrix , whose general form most nearly approaches that 
of Bunops , has a well-marked crest. Streblocerus , rotund in 
general form, has a slight keel on the dorsal side. Macrothrix 
latirostris has a decided keel, while M. rosea is practically de¬ 
void of one. Accmtholeberis and Ophryoxus are evenly rounded 
over the back, and are the most generalized of the family in 
general form. 
Bunops , while of compressed form, is not so greatly flattened 
laterally as is Daphnia. Its shape as seen from behind has 
the form of an isosceles triangle, the base being formed by the 
inflected ventral part of the valves. This structure also marks 
the high specialization of Bunops. In Ophryoxus , which comes 
ii—7 
