128 



Cincinnati Society of Natural History. 



Diaptomus eiskni Lilljeborg. 



Perhaps this should be considered a separate species or 

 variety, but it shows such marked resemblances, and I have 

 found so few specimens on which to base a description, that 

 it seems best not to separate it from the known form. It is 

 by far the largest species found near here, and is scarcely 

 equalled anywhere. The female measured 4.5 mm., and the 

 male 4 mm. in length. 



The first segment equals two-fifths of the whole length of 

 the cephalo-thorax. The others are nearly equal, except the 

 last, which is much shorter. It bears two small teeth at its 

 outer angles. 



The abdomen of the female is slender (Fig. 12). Its first 

 segment is equal to the rest of the abdomen and furca. It 

 bears quite prominent lateral teeth. It is very slightly dilated 

 anteriorily. The third segment is three times as long as the 

 second. The furcae are longer than broad and are ciliate along 

 both margins. 



The antennae of the female, which are a little shorter than 

 those of the male, reach only to the middle of the first ab- 

 dominal segment. 



The basal joint of the female fifth foot (Fig. 11) is nearly 

 triangular, and bears a seta at the outer angle. The inner 

 ramus is very slender, and is terminated by two spines, one- 

 third to one-half its own length. Including these spines it still 

 does not quite equal the first joint of the outer ramus. The 

 terminal joint of the outer ramus bears several teeth at the 

 inner edge, a plumose seta and two small spines on the outer. 



The antepenultimate joint of the male right antenna (Fig. 

 10) bears a hook as long as the last two joints and exactly 

 like that of the type. On the middle of the joint opposite the 

 hook is a peculiar seta, jointed at its middle, and at the same 

 time suddenly reduced in size. 



The basal joint of the right fifth foot of the male (Fig. 9) is 

 roughened on its inner aspect. The inner ramus is small and 

 about equal in length to the first joint of the outer ramus. 

 That joint is produced a little at its outer distal angle and 

 bears a small tubercle on its inner aspect. The terminal joint 

 bears a strong bent serrate spine at its distal third. The claw 



10 



