COPEPOD GENUS RIDGE WAYIA — WILSON 165 



comparable to the variously developed geniculations found in many 

 calanoid genera. 



Gurney (1927) and Ki-ishnaswamy (1953) have recorded non- 

 geniculate antennules in their specimens. In reviewing their ac- 

 counts in light of knowledge of these other species, it is difficult to 

 know how to assess their records. Both worked with limited material 

 (one or two specimens) and both presented their observations in a 

 very brief fashion. Giu-ney's description can only be considered in- 

 definite inasmuch as he referred to the joints as "rather indistinct." 

 In view of the observation made in my study that the geniculation 

 may easily be obscured in mounting, it does not seem unreasonable to 

 consider this character as inadequately known in these two species. 

 Since it may be of generic significance, it is an exceedingly important 

 character to reaffirm by critical observation of both mounted and un- 

 mounted material. 



The middle region of the male right antennule is not enlarged in 

 gracilis and shoemakeri, but there are modifications of some segments. 

 Segment 10 is shortened on the outer side. Segment 13 is even more 

 reduced on the outer side, and while remaining distinctly separated in 

 shoemakeri (fig. 30), it seems to have become partially fused with seg- 

 ment 14 in the specimens of gracilis that were critically examined. In 

 both species, segment 14 is elongate on the outer side. In gracilis 

 there is on the inner side a medial incision with sclerotized edges; the 

 sclerotization appears to extend into the internal part of the segment. 

 Beginning at this point in gracilis, and at a similar position in shoe- 

 makeri, there is a longitudinal muscle band that extends through seg- 

 ment 19. There is indication in Gurney's illustration of a modification 

 at the same point of the antennule of canalis, involving a reduction of 

 one segment and elongation of another, but no detail is given. 



Esterly did not mention such a modification of these segments in the 

 right antennule of marki. The antennule is described simply as "23- 

 jointed" with a "4-jointed terminal portion." The modified geniculate 

 portion of the antennule is illustrated, but unfortunately the figure 

 does not include all the succeeding terminal segments. There is a 

 question as to whether the "4-jointed terminal portion" was meant to 

 include only the segments beyond the geniculation, since the two 

 Tortugas species differ in having three or four segments beyond this 

 joint. This difference is apparently due to a fusion in gracilis of the 

 two segments immediately distad to the geniculation. This is shown 

 by comparison of the terminal segments of the two species (figs. 22, 

 29). The two distal segments correspond to one another in elongation 

 and in the number, placement, and length of the setae and aesthetes, 

 and so would appear to be of identical origin. In gracilis, the segment 



