ENTOMOSTRACA OF MINNESOTA. 47 
Heterocope, namely, is very near Epischura, both being restricted 
to fresh water. Diaptomus and Osphranticum are likewise only ac- 
cidentally found in the seas, though their nearest allies are marine. 
The genus Limnocalanus is as yet found in America only in the Great 
Lakes. 
In the distribution of genera we here follow Brady, whose defini- 
tion of the family Calanida, including Calanide and Pontellide of au- 
thors, we quote: ‘‘ Body elongated; composed of from ten to twelve 
[obvious] segments. Abdomen nearly eylindrical, much narrower 
than the cephalothorax and prolonged at the posterior extremity into 
two more or less cylindrical caudal branches [stylets]. First segment 
of thorax often anchylosed with the head; fourth and fifth segments 
also often coalescent. Head only rarely divided into two segments. 
Anterior antenne very long and composed of twenty-four or twenty- 
five joints; that of the right side in the male often modified for grasp- 
ing [geniculate]. Posterior antenne large, composed of a basal joint, 
from which spring usually two branches, the primary branch consist- 
ing of two, the secondary of several joints. Mandibles strongly 
toothed at the apex, palp (usually) two-branched. Mavxille strong, 
and provided with a many-lobed palp. Foot-jaws strongly devel- 
oped: first pair very broad; the basal joints having on the inner mar- 
gin wart-like processes, from which spring long ciliated bristles; the 
distal extremity divided into three short joints which are thickly be- 
set with strong and long, ciliated sete; second pair longer and more 
slender, basal portion forming two long oval joints; apical portion 
usually four-to six-jointed. First four pairs of feet two-branched, the 
outer branches always three-jointed. Fifth pair either like the fore- 
going, or much modified, unlike on the two sides, and in the male 
forming clasping organs. <A heart is present. Eyes either median 
and stalked or paired (lateral) and sessile; in the latter case being 
often coalescent and composed of several fences Sexual organs in 
the female symmetrical, in the male asymmetrical. Ovisac single, 
borne in front of [below] the abdomen. 
The Calanide are distributed over the whole globe, and yet the 
limitations of range are much more strict than in the other groups. 
Thus no species of the eastern continent has been positively identified 
in America, while the majority of the Cyclopidw of America are old 
world species or vicarious forms. 
Range of altitude is also limited, and the delicate organization of 
the Calanide responds to slight changes of the environment. The 
origin of our fresh-water genera from the marine forms in compara- 
tively recent times is on many accounts very probable. The forma- 
tion of large inland bodies of fresh water was an essential pre- 
