COPEPOD GENUS RIDGEWAYIA — ^WILSON 175 



are similar. The segmentation and armature of legs 1-4 are alike. 

 There is also some similarity in the fifth legs of the females, though 

 the distinctive modification of the exopod of Ridgewayia is not found 

 in Pseudocyclojis, and the endopod of Pseudocydoqys varies considerably 

 in segmentation and armature from species to species. If other char- 

 acters showed strong correlation, the differences in the female fifth 

 leg are such that they could well be considered generic rather than 

 familial. It is more difficult, however, to correlate the highly com- 

 plex male fifth leg of Pseudocydoi^s with that of Ridgewayia, though 

 relationship of the two genera might be assumed through the modified 

 endopods and the apical armature of the left exopod. 



In what are more easily comparable and, in part, more fundamental 

 characters, the two genera differ more widely. Important among 

 these is the contrast in the location of the paired genital openings of 

 the female. Those of Pseudocyclops are widely separated; those of 

 Ridgewayia, as exemplifi.ed by the two Tortugas species, are closely 

 set as in most other Calanoida. The antennule of Ridgewayia is 

 longer than that of Pseudocyclops, v/hich has the segments reduced 

 both in number and length so that the antennule is usually shorter 

 than tlie cephalic segment. In Pseudocyclops the right antennule of 

 the male is also more strongly geniculate and otherwise modified. 

 The rami of the antennae differ in their segmentation pattern. There 

 are strong resemblances in the mandible — the blades being very 

 much alike in the two genera and the palps differing principally 

 in the elongation of the basipod in Pseudocyclops. The maxillule 

 has the same number of elements, but in Pseudocyclops the distal 

 portions tend to elongation, and some parts have much more reduced 

 armature than found in Ridgewayia. There are very striking dif- 

 ferences in the structure of the maxillae and maxillipeds of the two 

 genera; in Pseudocyclops, the maxilliped is much reduced. In general, 

 the several differences of the cephalic appendages do not indicate an 

 extremely close relationship between the two genera. This, com- 

 bined with the difference in the location of the genital openings, 

 seems to exclude placement in the same family. On the other hand, 

 the likeness of habitus and habitat and the similarities of the legs 

 may indicate some degree of phylogenetic relationship. 



The group of species referred herein to the single genus Ridgewayia 

 have been shown to be in part inadequately known. The lack of 

 knowledge, however, is specific or generic. The species are quite 

 obviously referable to the same family. In the complete absence 

 of any other family in which they can be placed, and in liglit of more 

 complete knowledge than was available to former authors, it is 

 appropriate to propose for these species a new family, as follows : 



