144 TWELFTH ANNUAL EEPORT. 



palps of mandibles and maxillse usually well-developed; foot-jaws 

 mostly less developed than in Cala?iidce; first four pairs of feet as. 

 in Calanidce, fifth pair rudimentary, alike in both sexes, and usually 

 one- or two-jointed; ovisacs two. 



The circulatory system of this family is partly lacunal and has 

 heevx 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 

 Canthocamptus. 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 s^enera of the Cyclopidse here treated 

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

 *' common cyclops," 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 and to identif3^ such of the species as seem valid 

 and at the same time recognizable withoutreconditestudy of devel- 

 opment. Without 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. 



Auteniise 18-joiiitecl. 



8p. 1 . Cyclops eloiig-atus, Glaus. 



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

 than Claus, is distinguished from the C. pulchellus group by 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 setae. C elougatus lias 

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

 thus far by but a single author in Europe, appears in America, may 

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

 copepod is new. 



