446 Wisconsin Academy tof Sciences, Arts, and Letters. 



dite is indistinctly separated, is armed with two spines, and 

 there is a third spine on the second segment. This spinal ar- 

 mature was remarked by Forbes, but Schacht speaks of the third 

 segment as armed ^vith ''two or three spines." Schacht also 

 speaks of three spines in D. leptopus, and the figure of De 

 Guerne and Richard has three spines. In my statement, as 

 given before, I have said that there are only two spines in D. 

 leptopus, as that has uniformly been the case in the specimens 

 I have examined. It is very possible that this is a variable 

 feature, and while I have considered this one of the points of 

 difference of the variety, I think it very likely that it is not a 

 matter of even varietal distinction. The second segment of the 

 abdomen in D. piscinae, I have found considerably longer than 

 in typical D. leptopus. 



It seems to me that these differences are so slight that they 

 certainly should not be considered specific, and it is a question 

 whether they should even be thought enough to constitute a 

 variety. I have no doubt that further collections will bring 

 to light connecting forms, but it may be best, for a time at 

 least, to retain the varietal name. 



DiAPTOMus stact]s^alis Forbcs. 

 Plate XXVII, figs. 3, 6, 7. 



1882. Diaptomus stagnalis Forbes, p. 646 ; pi. VIII, figs. 8, 



10, 11, 12, 14. 



1882. Diaptomus giganteus Herrick, p. 222 : pi. II, figs. 3, 



11, 15. 



1884. Diaptomus stagnalis Herrick, p. 139 ; pi. Q, figs. 11, 13. 

 1889. Diaptomus stagnalis DeGuerne and Richard, p. 23 ; figs. 



15, 16; pL IV, fig. 14. 

 1895. Diaptomus stagnalis Herrick and Turner, p. 66 ; pi. Ill, 



figs. 1-12 ; pi. XIII, figs. 11, 13. 

 1897. Diaptomus stagnalis Schacht, p. 138; pi. XXVIII, 



fig. 2. 



''Head distinct from thorax; fifth and sixth thoracic seg- 

 ments confluent. Lateral angles of last thoracic segment strongly 



