146 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



CLASSIFICATION OF THE CLADOCERA. 



SUB-ORDER I.— CALTPTOMERA (membrane-clothed). 



Teibe I. — Ctknopoda. Families: Sidide, Holopedidie. 



Tribe II. — Anomopoda. Families: Daphnidse, Bosminidx,Lyncodaphnidse, LynceidsB- 



SUB-ORDER II.— GYMNOMERA (destitute of coTerin^). 



Families: Polyphemidse, Leptodoridse. 



FAIIILY SIDIDE. 



Head separated from tlie body by a depression, witliout prominent 

 fornices (or spreading shields) over the base of the antennae. First 

 pair of antennte, or antenniiles, as we shall uniformly call them, one- 

 jointed, usually rather small in the female, but extending into a very 

 strong flagellum in the male. AntenniB long, biramose, with unequal 

 branches. Mandibles truncate at the end. Maxillse armed with large 

 spines. The form is usually elongate, and the abdomen often extends 

 beyond the edge of the shell behind. The male openings are usually 

 in the end of long appendages which depend from the base of the post- 

 abdomen. This interesting family is represented in America so far 

 by four species, one of which constitutes a new genus. Others will 

 undoubtedly be found upon a careful study of the fauna of the Great 

 Lakes. Most of the species prefer the clearer and colder water of 

 large lakes. The processes of development, as traced by the writer, 

 vary very little from the method exhibited by Moina. The ephippial 

 condition, however, is not found in these animals which are less sub- 

 ject to destructive inflaences of the climate. They do, however, pro- 

 duce so called winter eggs, which are laid in October and are distin- 

 guished from the summer eggs, which hatch in the brood cavity, by a 

 brown color and the presence of fatty spheres. These eggs are pro- 

 duced in large numbers in distinction from most other Cladocera^ in 

 which the winter eggs are very few. These eggs are permitted to 

 settle to the bottom and there develop at the proper time. Sida cnjs- 

 talUna is often found in immense numbers in large lakes which contain 

 abundant plant growth. The size, and especially the reproduction 

 activity, is very dependent on the environment, and hence little suc- 

 cess is obtained in preservation in aquaria. Some of the genera are 

 nocturnal and should be sought at the surface on quiet evenings. 



GENUS SIDA Straus. 



Body elongate, hyaline. Head small, quadrate. Fornices absent. 

 Antennules of female small, truncate; of male, with a long flagellum. 

 Second antennoe with the rami two- and three-jointed. Male with the 



