Marsh—North American Species of Diaptomus. 445 
1.4 mm. Schacht’s measurements are somewhat larger—viz., 
female, 1.89 mm, and male, 1.83 mm. The differences, in 
these measurements are not very qTeat, and probably arise from 
the measurement of a comparatively small number of speci¬ 
mens in each case. 
This species seems to be generally distributed through the 
Mississippi valley. 
diaptomus leptopus vai\, piscinae Forbes. 
Plate XX, figs. 3, 6, 8. Plate XXI, fiq*. 7. 
1893. Diaptomus piscinae Forbes, p. 253; pi. XLI, fig. 22. 
1895. Diaptomus piscinae Herrick and Turner, p. 74; pi. V, 
fig. 13. 
1897. Diaptomus piscinae Scliacht, p. 125 ; pi. XXII, figs. 1-4. 
The original description of this form by Forbes was from 
specimens obtained from a small lake near Gardiner, Montana. 
Schacht reports it in collections from Portage Slough, Mani¬ 
toba. I have found it in collections made by Mr. Congdon in 
Birch Hills, Alberta, and in material sent by Mr. Juday from a 
lake on the University campus in Boulder, Colorado. The 
points of difference made by Forbes to distinguish this from D. 
leptopus are the length of the setae on the endopodite of the 
female fifth foot, the more slender form of the fifth feet of the 
male, and the absence of the antennal hook. These differences 
undoubtedly exist with the exception of the absence of the an¬ 
tennal armature. I find in all my specimens the hyaline la¬ 
mella of the antepenultimate segment of the right male antenna 
just as in D. leptopus, but not quite so pronounced. Professor 
Forbes kindly loaned me some slides of D. piscinae, and in the 
only one which showed the male antennae the hvaline lamella 
was present, though the antenna was turned so that it might 
easily escape notice. 
I have noticed certain other points of difference between the 
two forms. The endopodites of the male fifth feet are consid 
erably longer in D. piscinae. The third segment of the exopo- 
