164 PROCEEDINGS OF THE NATIONAL MUSEUM vol. los 



Although admittedly an obvious point, it does seem apropos to 

 stress the desu-ability of including results of detailed critical examina- 

 tions of the antennules in published records of any specimens of 

 Ridgewayia or of allied genera. The discovery of two species of 

 Calanoida with 26-segmented antennules is a matter of considerable 

 systematic interest. Such an unusual segmentation might be an 

 important part of a generic definition. In the present instance, it 

 cannot separate the Tortugas species generically from Ridgewayia 

 typica because the otherwise obviously related Bermuda species 

 marki is said to have a 25-segmented antennule. If this is actually 

 the case, then the difference in segmentation must be considered 

 specific. However, on the basis of their descriptions, it is not in- 

 appropriate to suggest that there is need to verify whether the anten- 

 nules of typica and marki are really 25-segmented, and, if so, how their 

 armature compares with that of gracilis and shoemakeri. Esterly 

 (1911) gave no detail of the female or left male antennules in his ac- 

 count of marki. The antennule is figured for typica; it shows a very 

 elongate second segment, and three elongate distal segments. It is 

 personally considered doubtful if the setation shown is entirely exact. 

 There are two setae on nearly every segment but there is no distinc- 

 tion between setae and aesthetes, and many of the setae shown are too 

 similar in length to have been based on exact observation. 



Considered critically, it cannot be judged from the text of Gurney's 

 description of Suezia canalis whether or not the segmentation given 

 applies to both of the antennules or only to the right. No direct 

 reference is made to that of the left side. If the statement "1st 

 antenna of 21 or 22 joints" refers to both antennules, then the seg- 

 mentation within this group of species varies over the considerable 

 range of from 21 to 26 segments. 



In the specimens observed, the geniculation of the male right 

 antennule is only moderately developed. It was noted while working 

 with the Tortugas material that the antennule could be tm-ned or 

 mounted in such a way that the jointing becomes obscured. There 

 exists, however, as illustrated for the two Tortugas species and as 

 shown by Esterly for marki, a real constriction between two of the 

 distal elongate segments. In whole specimens (most advantageously 

 observed in alcohol), the distal part of the antennule is frequently bent 

 upwards or outwards at this joint as is characteristic of geniculate 

 antennules. This modification as it occurs in these species of Ridge- 

 wayia, though weak, is obviously a specialized joint, giving to the 

 distal portion of the antennule a unit flexibility and freedom of move- 

 ment not present at any other part of the appendage. Such a spe- 

 cialized joint may be presumed to be functionally and structurally 



