54-0 On some Entomostraca of Lake Michigan rjuly, 



bay, in the north-eastern part of Lake Michigan, and in the south 

 end of the lake off Chicago and Racine. Several of the lacus- 

 trine species had been previously received from Mr. B. W. 

 Thomas and Mr. Chas. S. Fellows, of Chicago, by whom they 

 had been strained from the Chicago water supply. 



A few additional species from the lakes and pools of Central 

 and Northern Illinois, are described in the appendix to this paper, 

 one of which occurs also in Southern Massachusetts, and prob- 

 ably throughout the country intervening. 



* One of the most interesting species was obtained in consider- 

 able numbers in Grand Traverse bay, associated with the ordinary 

 forms of the lake, nearly all of which were abundant there in 

 October, 1881. It is a copepod of the family Calanidae, repre- 

 senting a new genus and species, for which the name Epischura 

 lacuslris is proposed (PL ix Fig. 8, and PI. vm Figs. 15, 16, 

 21-23 an d 25-27). 



The family is easily distinguished from Cyclopidae and Har- 

 pactidae, to which most of our other fresh-water species belong, 

 by the elongate anterior antennae of 23-25 articles, by the (usu- 

 ally) two-branched antennulae and mandibular palpi, by the wide 

 difference in size between the abdomen and thorax, and by the 

 fact that in the male only one antenna is converted into a clasping 

 organ. Epischura is colorless in autumn, although possibly red m 

 spring, .063 in. long by .015 in. wide, and distinguished in both 

 sexes by what seems at first a deformity of the abdomen. On 

 closer inspection it is seen that in the male the last three segments 

 of this region are laterally produced into a grasping organ of 

 peculiar construction, and that the whole abdomen is thus dis- 

 torted and rendered unsymmetrical. The lateral processes of the 

 first and second segments evidently act against each other as a 

 powerful pair of nippers, while the third, bearing upon the same 

 side a stout toothed plate, must greatly increase the security of 

 the grasp, when brought into play by the strong muscles of the 

 abdomen. A fourth process extending forward from near the base 

 of the right ramus of the furca, also contributes to the formation 

 of this organ. A steel-trap attachment to the tail of an alhgatoi 

 would very well illustrate the vigorous embrace of this little 

 crustacean. Besides this, the right antenna is thickened and 

 hinged as a clasper, and the last pair of legs is also convert 

 into a complicated apparatus of claws and forceps. In the a 



