46 PROCEEDINGS OF THE ACADEMY OF [Jan., 



ence from the European forms. The three terminal joints are 

 slightly curved and each bears a well-developed hyaline plate. The 

 edges of these plates, which Forbes found to be entire, seem to vary. 

 I have frequently found them finely serrated on the distal third of 

 the terminal segmental plate. Again I have noted a very distinct 

 notch or indentation at the posterior end of the serrations. This 

 resembles somewhat the characteristic "notch" in the corresponding 

 plate of Cyclops leuckarti Claus, though it is not so deep nor con- 

 spicuous. Occasionally I have observed a specimen in which all 

 three hyaline plates were finely serrated. The commonest form has 

 two of the plates with smooth edges, though the plate of the last 

 segment invariably has the slight notch mentioned above (PI. Ill, 

 fig. 3). 



The very long and strong setae on the first and fourth antennal 

 segments and the change of direction of the remaining segments 

 beyond the fourth, as well as the short caudal stylets, suggest a 

 superficial resemblance to Cyclops modestus Herrick, 



The four pairs of swimming feet are armed as follows : 



First pair — outer ramus, three spines, five setae; inner ramus, one 



seta, one spine, four setae. 

 Second pair — outer ramus, four spines, five setae; inner ramus, six 



setae. 

 Third pair — like second. 

 Fourth pair — outer ramus, three spines, five setae; inner ramus, one 



seta, one spine, three setae. 



Both the spines and setae of these feet are peculiarly long and 

 slender. 



The rudimentary fifth foot (PI. Ill, fig. 4) consists of a single seg- 

 ment, armed with a spine and two setae. The spine is inserted 

 immediately above the characteristic bulge of the minutely plumose 

 inner side. The longer of the two setae is borne at the end of a cone- 

 shaped projection of the distal end of the segment. The remaining 

 seta is inserted on the outer side of the segment at the base of the 

 cone-like process. Its length is two-thirds that of the apical seta 

 and slightly greater than that of the spine. Both the setae are 

 delicately plumose; the spine is more coarsely so. Brewer notes that 

 the "three setae" are bare in his specimens. 



The form of the receptaculiim seminis (PI. Ill, fig. 5) is the most 

 characteristic feature of this species, though it is frequently quite 

 difficult to distinguish owing to the density of the pigment matter 

 in the first abdominal segment. It consists of two very distinct 



