Marsh— North American Species of Diaptomus. 445 



1.4 mm. Scliacht's measurements are somewhat larger — viz., 

 female, 1.89 mm^ and male, 1.83 mm. The differences in 

 these measurements are not very qreat, 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 var. PISCINAE Forbcs. 



Plate XX, figs. 3, 6, 8. Plat« XXI, fia'. 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 Schaeht, 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. 

 Schaeht 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 

 imdoubtedly 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 pronomiced. 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- 



