446 Wisconsin Academy \of Sciences , Arts 9 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, hut Schacht speaks of the third 
segment as armed with “two or three spines. 7 * 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 stagxalis Forbes. 
Plate XXVII, figs. 3, 6, 7. 
1882. Diaptomus stagnalis Forbes, p. 646; pi. VIII, figs. 8, 
10, 11, 12, 14. 
1882. Diaptomus gig ant eus 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; pi. 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 
