18 '2 Illinois State Lahoratory of Natural History. 



Just without these, on the second segment, is a third spine, 

 shorter than either of the other two. 



Inner ramus of fifth leg of female one-segmented, extend- 

 ing beyond the end of the first segment of the outer ramus ; 

 apex hairy ; armed with two long suhequal spines hairy on 

 both margins and about a third the length of the ramus. 



Length of female 1.89 mm. ; of male 1.83 mm. 



Breadth of female 0.70 mm. ; of male 0.60 mm. 



The numerous published figures and descriptions of this 

 species have probably made it well known to all students of 

 North American Centropag'uhe. The synonymy, however, is 

 interesting. In the Geological and Natural History Survey 

 of Minnesota, Herrick ('77, p. 238) describes and figures 

 "A New Cyclops." It is evident at a glance that this is a 

 Diaptomus, but of what species cannot be determined. In 

 "Microscopic Entomostraca " (Herrick, '79, p. 90) he refers 

 to this "Cyclops" and says, "In the Report of the Geological 

 and Natural History Survey of Minnesota for 1878 it 

 [Dlaptomns lou</i('or)i'is] was mentioned and a figure given, 

 but erroneously called Cyclops ^ In a "Final Eeport on the 

 Crustacea of Minnesota " (Herrick, '84, p. 140) he makes D. 

 Icptopns Forbes a variety of D. longicornis Herrick, estab- 

 lishing a second variety, slmUis (Plate Q, Fig. 5-7). In his 

 " Synopsis of the Entomostraca of Minnesota" (Herrick and 

 Turner, '95) he recognizes D. leptopus Forbes as a distinct 

 species, making 7). louyicornis var. leptopus a synonym ; 

 although in this same work 1). longicornis var. shniUs Her- 

 rick is not set up as a species, neither is the name regarded 

 as a synonym. The figures (Herrick '84, PI. Q, Fig. 5-7) are 

 not well drawn, but it is not likely that this form is leptopus, 

 1). slniilis is referred to once (Herrick and Turner '95, p. 58) 

 in connection with T>. franclscanus Lilljeborg. Diaptomus kcn- 

 tuckyensis Chambers ('81) is also quite possibly D. Iep)t02nis, 

 although the description is very vague and the figures are 

 inaccurate. 



