ENTOMOSTKACA 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 Limnoealanus 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 Calanidw, including Calmiidce and Fontellidce of au- 

 thors, we quote: "Body elongated; composed of from ten to twelve 

 [obvious] segments. Abdomen nearly cylindrical, 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 antennte 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 antennae 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. Maxillse 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 setae; 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 lenses. Sexual organs in 

 the female symmetrical, in the male asymmetrical. Ovisac single, 

 borne in front of [below] the abdomen. 



The Calanklce 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 Cyclopidce of America are old 

 world species or vicarious forms. 



Range of altitude is also limited, and the delicate organization of 

 the Qdanida' 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- 



