North American Species of Diaptomus. 175 



compared with the remainder; lower two thirds very minutely 

 spinose ; tip sometimes slightly recurved. 



Inner ramus of right fifth foot one-segmented, narrowing 

 but slightly toward the tip. It reaches almost to the middle 

 of the last segment of the outer ramus, but not to the hook- 

 like process. Apex rounded ; unarmed or very delicately 

 hairy. 



Outer ramus of the left fifth foot two-segmented. First 

 segment irregularly trapezoidal ; small and inconspicuous, 

 with a delicately hairy cushion-like process on the inner mar- 

 gin. Last segment consisting of two digitiform processes, 

 forming a forcipate structure. Seen from behind, the upper 

 process is smooth, the base slightly swollen. It is a little longer 

 than the other and about one and a half times as long as the 

 preceding segment, tapering gradually from the thickened 

 part to an obtuse point. The lower process (seen from behind) 

 is about equally broad at the base and at the beginning of the 

 last third, whence it narrows quite suddenly to form an obtuse 

 point. It is provided within and at the apex with four or 

 five small teeth. 



Inner ramus of left fifth foot paddle- shaped, considerably 

 broadest at the apex ; reaching almost to the tip of the outer 

 ramus ; either smooth or very delicately hairy. 



Length of female, 1.2 mm. ; of male, 1.1 mm. 



Most of the specimens examined were taken from Lake 

 Maitland, Florida, from material kindly loaned me by Mr. 

 Adolph Hempel. 



The above was prepared as a description of a new species, 

 but when I saw Professor Marsh's slides there was no longer 

 any doubt as to the identity of mississippiensis and this Florida 

 form. Prof. Marsh ('94) figures the furca of the female as 

 perfectly smooth within, while in all of the specimens from 

 Florida, as well as in those which he kindly loaned me, they 

 are distinctly, though not heavily, setose within. The inner 

 rami of the fifth pair of feet in the male, however, differ con- 

 siderably — probably a varietal difference, since in a few of my 

 specimens they approached the form shown in his figures. 

 In the Florida specimens I fail to find the asymmetry in the 



