1914.] NATURAL SCIENCES OF PHILADELPHIA. 25 



States. Forbes states that "it has been found in Massachusetts 

 and Wyoming and in all the intervening territory," and further that 

 "it is the commonest Cyclops in the Great Lakes." Miss Byrnes 

 has recently found it to be a common form in the Long Island waters. 

 I have noted that it occurs very abundantly in one of the large 

 streams in this vicinity, but in the small pond from which I have 

 taken every other species described in this paper I have found but a 

 single specimen.^ 



Specific Description. — In the specimens of C. hicuspidatus Claus 

 from this vicinity, the lateral angles of the cephalothorax are very 

 prominent, as in the "specimens from the far west" (Forbes). The 

 first thoracic segment is a little more than half the length of the 

 entire cephalothorax (PI. II, fig. 1). The posterior borders of all 

 the thoracic segments are smooth. 



The first abdominal segment (PI. II, figs. 1 and 5) is unusually 

 expanded, laterally, on the anterior side of the suture. It is about 

 as long as the remaining three abdominal segments. The posterior 

 margins of the first three abdominal segments are finely serrated 

 (PI. II, fig. 5). The fourth segment has the usual row of spinules 

 on its posterior margin (PI. II, figs. 1 and 2). 



The stylets (PI. II, fig. 2) are more than twice as long as the last 

 two abdominal segments. Their length is about six times their 

 width and they are frequently slightly out-curved. The above 

 proportions hold good only in the cases of the specimens examined. 

 They vary considerably in different localities. The lateral spine is 

 inserted at the beginning of the posterior third of the ramus, and at 

 a distance of about one-quarter of the length of the stylet from its 

 insertion point there is always present a minute lateral comb of 

 spinules (PI. II, fig. 2). Of the apical setae, the outermost is heavy, 

 finely plumose, and about as long as the delicate inner seta. The 

 longer of the two prominently developed setae is about equal in 

 length to the abdomen and twice that of the shorter seta. The}' 

 are both delicately plumose. 



The first antennae of the female (PI. II, fig. 1) are seventeen- 

 jointed and terminate at the end of the first thoracic segment. At 

 the distal end of the twelfth segment there is borne an unusually 

 long, spear-shaped sense-club (PL II, fig. 3). The setae are all quite 

 short and plumose for the most part. The terminal segments bear 



^In late March and April, 1910, collections in the vicinity of Cambridge. 

 Mass., this was by far the most abundant form. 



