X(/itli A)turn-iiit C'ciitrop(ig'ul«'. 2'27 



ing character in the CopepixJa. If this he taken as a hasis 

 of chissification here, O.yiJn-diiticiiiii, with its 23-segmeiited 

 antenn;t, wouhl form a gronj) l)y itself, while Lhnnocalanus, 

 DiapfoiitKs, and Kpl^ichuid, with their 2 5 -segmented antcnnsr 

 would constitute another group. 



Osphnutt'icnm seems to he the most primitive of the Amer- 

 ican Centro])(tf/i(1(e, the fifth legs especially heing less differ- 

 entiated than in any of the other genera. This is particularly 

 true of the female, in which all of the legs are biramose, each 

 ramus consisting of three segments. In the male the left 

 fifth leg is similar to the preceding legs, hut the right one has 

 a two-segmented outer ramus, the second segment being ap- 

 parently formed by the coalescence of the second and third 

 segments. In both sexes the inner rami of all the pairs of 

 legs are alike. 



Liunioealanufi apparently approaches most closely to Os- 

 plirntitlruni, the fifth pair of legs of the female being very 

 similar in general structure to those of 0>>plir<(ntlcu))i, as is 

 perhaps most strikingly illustrated in the case of L. iiKicni- 

 rus Sars and 0. lahyoiiectnm Forbes. In I/nnnocalanu^ both 

 rami of the four anterior pairs of legs in both sexes are three- 

 segmented and but slightly modified, as are also those of the 

 fifth pair of legs of the female ; but in the latter the second 

 segment of the outer ramus is produced on the inner margin 

 into a hook-like process, as in Osplirant'icnm. The inner 

 rami of the fifth pair of legs of the male are still three- 

 segmented and similar to those of the preceding legs, but the 

 outer rami are modified and are two-, or indistinctly three-, 

 segmented. 



I>i((pt()niiis is perhaps next in respect to modification. 

 In this genus all the legs are biramose, but the first pair con- 

 sists of a three-segmented outer, and a two-segmented inner, 

 ramus. The following three pairs have* both rami three-seg- 

 mented. In the female the fifth pair of legs has a two- or, 

 more rarely, three-segmented outer ramus, and a one- or, 

 occasionally, two-segmented inner ramus. In the male the 

 inner ramus is one- or, rarely, two-segmented, while the outer 

 ramus of the right leg is three-segmented and that of the left 

 leg two-segmented. 



