STATE GEOLOGIST. 19 



FaM. 1. — PoLYPHEMIDiE. 



Abdomen curved, terminating in two long stylets. 



Fam. 2. — Leptodorid^. 



Abdomen straight, ending in short claws. 



FAMILY SIDIDiE. 



Head separated from the body by a depression, without promin- 

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

 First pair of antennae, or antennules, as we shall uniformly call 

 them, one-jointed, usually rather small in the female, but extend- 

 ing into a very strong flagellum in the male. Antennae long, 

 biramose, with unequal branches. Mandibles truncate at the end. 

 Maxillae 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 ap- 

 pendages 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 

 subject to destructive influences of the climate. They do, how- 

 ever, produce so-called winter eggs which are laid in October and 

 are distinguished from the summer eggs, which hatch in the brood 

 cavity, by a brown color and the presence of fatty spheres. These 

 €ggs are produced in large numbers in distinction from most other 

 €ladocera 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 crystallina is often found in immense numbers in large 

 lakes which contain abundant plant growth. The size, and especi- 

 ally the reproduction activity, is very dependent on the environ- 

 ment, and hence little success is obtained in preservation in 

 aquaria. Some of the genera are nocturnal and should be sought 

 at the surface on quiet evenings. 



I. — GrENUS Sida. Straus. 

 (Plate N. Figs. 12-14.) 



Body elongate, hyaline. Head small, quadrate. Fornices ab- 

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



