146 "GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
CLASSIFICATION OF THE CLADOCERA. 
SUB-ORDER I.— CALYPTOMERA (membrane-clothed). 
TRIBE I.—CTENOPODA. Families: Sidide, Holopedide. 
TRIBE IJ.—ANOMOPODA. Families: Daphnidx, Bosminidx, Lyncodaphnide, Lynceide. 
SUB-ORDER II.—GYMNOMERA (destitute of covering). 
Families: Polyphemidz, Leptodoride. 
FAMILY SIDIDE. 
Head separated from the body by a depression, without prominent 
fornices (or spreading shields) over the base of the antenne. First 
pair of antenne, or antennules, as we shall uniformly call them, one- 
jointed, usually rather small in the female, but extending into a very 
strong flagellum in the male. Antenne long, biramose, with unequal 
branches. Mandibles truncate at the end. Maxille 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 influences 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 crys- 
tallina 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 antennz with the rami two- and three-jointed. Male with the 
