North American Frcsh-icaicr Cyclopidie. 39 



Cragin in 1883 figured a form as C. riridts and stated that 

 it was found at Cambridge, Mass. This form is ('. in.scctHs. 

 C!ich)]>>i iiii'Kdifiiiliitiix, described as new in the same article, is 

 also C. iiiscctiis, the only apparent difference being a very 

 slight one in the armature of the swimming feet. 



Ci/rl()])s ])vcr'i^p'iii<)Hus, described in 1884 by Herrick, differs 

 from ('. insect itii principally in the shape of the outermost 

 terminal spine of the stylet. In the type of hrerUp'niosns this 

 spine is very broad, heavy, and knife-like in character. I have 

 seen considerable variations in the shape of this spine and 

 have observed all of the gradations l)etween it and the usual 

 slender spine of ('. insect us. I think, however, that C. hrevi- 

 sp'niosiis should be considered as a good variety. The follow"- 

 ing description of C. rirldls is a translation of the description 

 l)y Schmeil ('92). 



SPECIFIC DESCRIPTION. 



"The two axes of the cephalothorax compare about as two 

 to one ; the ratio of the length of the cephalothorax and the 

 abdomen is almost the same. The cephalothorax tapers about 

 equally in both directions; each segment projects laterally 

 far beyond the following. Seen from the side, the posterior 

 angles of all the plates of the cephalothoracic segments are 

 rounded, those of the first and fifth segments being at first 

 straight, then convexly produced at their ends ; and the 

 second, third, and fourth segments, in which such x)romi- 

 nences are lacking, are slightly lengthened posteriorly. 



" The first abdominal segment is but little broadened in its 

 anterior part. The posterior borders of all the segments are 

 coarsely serrate, with the exception of the last, which bears 

 a fringe of spinules. 



"The stylets are often two, three, or even four times as long as 

 the last abdominal segment. The inner border is always ciliate. 

 The lateral spine is set beyond the middle of the outer edge. 

 The outermost of the apical bristles (all of which are nar- 

 rowly plumose) is not, as is the case with most species, 

 changed into a spine, and is exceeded in length by the inner- 

 most. Both middle bristles are well developed, but their 



