640 On some Entomostraca of Lake Michigan [August, 



ON SOME ENTOMOSTRACA OF LAKE MICHIGAN 

 AND ADJACENT WATERS. 



BY S. A. FORBES. 



( Conl: 'nber.) 



A THIRD Calanid deserves special mention as a species of Lim- 

 nocalanus, a genus known hitherto only from Scandinavian 

 lakes. It is readily distinguished, without dissection, from the other 

 fresh-water Calanidae, by the extraordinary length, size and promi- 

 nence of the five or six terminal setae of the first maxillipeds. The 

 second maxillipeds are also very long. The legs are all bi-ramose, 

 the inner ramus of the fifth pair resembling the same appendage 

 of the other legs. This species, which may be Limnocalanus 

 macrurus Sars, was first sent me by Mr. C. S. Fellows, of Chica- 

 go, about four years ago, a mutilated female having been obtained 

 by him from the city water supply. The furca is as long as the 

 entire abdomen. The rami are hairy, parallel, about seven times 

 as long as wide, and provided with five subequal terminal setae, 

 and one some distance in front of the external angle. It has been 

 collected thus far only in the south end of the lake. I have found 

 it abundant in the city harbor, even in the polluted water near the 

 mouth of the river, where it is associated especially with Diapto- 

 tnus sicUis and the Cyclops next to be described. 



The Calanidae seem to have an unusual development in this 

 country ; and to facilitate their study and comparison, I have de- 

 scribed further on all the species which I have hitherto clearly 

 distinguished. 



Smallest and most abundant of the Copepoda of the lake, is a 

 minute Cyclops ( C. thomasi, n. s., PI. ix Figs. 10, II and 16), only 

 four hundredths of an inch in length (without setae) and about 

 eleven thousandths of an inch in width, slender and colorless, with 

 remarkably long caudal stylets ; and especially noticeable for the 

 great difference in the length of .the caudal setae. The inner an 

 outer ones are inconspicuous, while the outer of the two median 

 setae is longer than the furca, and the inner of these two is as 

 long as the whole abdomen. This Cyclops was first receive 

 from Mr. B. W. Thomas, and I have since found it excessively 

 abundant in the lake. I have not encountered it, however, in any 

 other waters. 



Its nearest European ally is apparently Cyclops bicuspid** 



