North American Fresh-water CyclopiUce. 



55 



It is also my opinion that Brady's variety montanus should 

 be considered as merely a variation of the typical form. 



SPECIES DESCRIPTION. 



The cephalothorax (PL XVII.) is quite regular in shape, 

 being almost exactly elliptical in outline. Its segments 

 are closely joined and its lateral outlines smooth. The fourth 

 segment is deeply excavated behind and is usually bordered 

 by fine sharp teeth or by long hairs. 



The abdomen (PL XVII., and PL XVIII., Fig. 1) is broad 

 in front, but narrows so rapidly posteriorly that the greater 

 part of the first segment is as narrow as the slender segments 

 following. Behind the enlargement of the first segment the 

 abdomen tapers very little. The last segment is bordered 

 posteriorly by the usual row of spinules, and the preceding 

 segments by fine sharp serrations. The stylets are commonly 

 about straight, but are occasionally strongly outcurved and 

 divergent. Their length to breadth varies from 1 : 1.8 to 1:9 

 but 1 : 4 is the commonest proportion. A row of spinules, 

 spines, or curved hooks marks the outer border of each stylet 

 and extends from its base to the point of insertion of the outer 

 apical spine, near the posterior end. These projections in- 



