182 Illinois State Laboratory of Natural History. 



to find a word in addition to the following. Speaking of D. 

 siciloides, he says: "This species approaches J>. sicilis 

 Forbes and I). caroli Herrick very closely, and is said also to 

 resemble D. gracilis Sars. From caroli it may be at once dis- 

 tinguished by reason of the fact that the third joint of the 

 outer ramus of the fifth foot of the female is obsolescent." 

 The " D. caroli Herrick" would lead one to suppose that it 

 had been described before ; but, although this work contains 

 the names and short descriptions of all the other species, 1). 

 caroli is not among them. I doubt, therefore, whether I am 

 justified in putting it even under the head of "insufficiently 

 described" species. 



Diaptomus longicornis var. similis Herrick. 



Diaptomus longicornis var. similis, Herrick, 1884. p. 141, PL Q, Fig. 



5-7. 

 Diaptomus similis. Herrick and Turner, '95, p. 58. 



Something has already been said in regard to this doubtful 

 species under the head of D. lejptopus. First mentioned in 

 Herrick's "Final Keport," as one of two varieties, — the other 

 being the true leptopus as acknowledged by him ('95a), — it 

 is not mentioned again except in the description of D.francis- 

 canus, where he says "The form of the fifth feet chiefly sepa- 

 rates this species from Diaptomus similis Herrick." This 

 species cannot stand until a more complete description is 

 written. 



DISTRIBUTION OF THE AMERICAN SPECIES OF DIAPTOMUS. 



I), sicilis Forbes is one of the most common species in the 

 Great Lakes, and has been found in Wisconsin, Michigan, 

 Minnesota, and Yellowstone Park. In Illinois it is recorded 

 from Cedar Lake and Fox Lake. 



D. piscinae Forbes has been recorded only from Yellowstone 

 Park, and I now add Portage Slough, Manitoba, Can. 



D. lintoni Forbes has been found only in Yellowstone 

 Park. 



I), leptopus Forbes is found in Massachusetts, Wisconsin, 

 Minnesota, and Illinois. 



