144 TWELFTH ANNUAL REPORT. 



palps of mandibles aud maxillge usually well-developed; foot-jaws 

 mostly less developed than in Calcniidce; first four pairs of feet as 

 in Calanid(e,&fth. pair rudimentarj', alike in both sexes, and usually 

 one- or two-jointed; ovisacs two. 



The circulatory system of this family is partlj' lacunal and has 

 been thought to be entirely so in the genus Cyclops, closer obser- 

 vation, however, shows that there is something like an imperfect 

 central organ at the point occupied by the heart of higher Cope- 

 pods. This was figured in my previous report, plate V, fig. 1, but 

 no mention was made of the discovery. It has since been verified. 

 The apparatus referred to is a modification of that described under 

 Cauthocamptus. In the second thoracic segment there is a set of 

 swaying membranes which constitute a valvular apparatus, chiefly 

 moved by the action of the stomach. 



Genus Cyclops. 



The sole representative of the genera of the Cyclopidae here treated 

 is the best known of the Copepoda. Every one is familiar with the 

 " common CN'clops," but few realize how many are the species in- 

 cluded under this name. An attempt is here made to enable the 

 student to recognize the more obvious distinctions upon which the 

 genus is subdivided aud to identify such of the species as seem valid 

 and at the same time recognizable withoutreconditestudy of devel- 

 opment. AVithout attempting a complete elucidation of the syn- 

 onymy, which is practically an impossibility, a proximate classifica- 

 tion of all the species known to me is attempted. Thirty suffici- 

 ently well marked species are enumerated, and the position of a 

 number more is indicated. 



Anteniiie 18-jointecl. 



Sp. 1 . Cyclops elougatus, Claus. 



This species, cited hitherto, apparently, by but one other author 

 than Claus, is distinguished from the C. pulchellus group bj'' the 

 18-jointed antennae, which are hardly longer than the first thoracic 

 segment. The caudal stylets are longer than the two preceeding ab- 

 dominal segments, and bear rather short setas. C. elougatus has 

 been found by Cragin near Cambridge. That this species, found 

 thus far by but a single author in Europe, appears in America, ma\' 

 serve as a warning not to decide too hastily from its habitat that a 

 copepod is new. 



