46 COPEPODA 



Of this species Giesbrecht has only examined a single mutilated male from the Pacific Ocean. 

 The figure, which is represented on his pi. 9 fig. 14 is not quite like the structure found in several 

 males which I have examined, the main-differences being that the endopodite of the right leg in none 

 of my specimens is terminated with a short clumsy hair; it is rather doubtful if this difference has any 

 specific value, as the legs of the animals examined show marked variations in other respects. The 

 left leg consists of 2 basal segments and a fairly elongate exopodite (fig. 4g) produced into a more or 

 less curved terminal spine and a minute Se; only in a single one of my specimens, which had no Se, the 

 St was so strongly curved as figured by Giesbrecht (fig. 4h). In the four specimens examined the 

 exopodite of the right leg had a long St and a short slender Se; but the endopodite varied in a 

 curious way. In a specimen (fig. 4g) with the Ri about 5 times as long as wide, the articular line 

 between the last two segments was almost obsolete, and the posterior surface was more hairy than in 

 the specimen with the segment about 3-6 as long as wide (fig. 4h). In a single specimen (fig. 4J) the 

 Ri was represented by short segment, but this is probably due to a mutilation. 



Y. . <? (St. V). Size: 3-5 4-1 mm. The "head" is about twice as long as the thorax, and the 

 anterior division is 5-5 as long as the abdomen, which consists of four somites; the last one is partly 

 fused with the furca; the first (genital) somite is produced beneath in the female, not in the male. 

 The appendages are in most respects alike those of the mature females; the only difference of any 

 interest is, that the exopodite of the maxillulae possesses 8 instead of 9 bristles. While the fifth pair 

 of legs in the female is like that of the mature, this organ is in the male less developed than in the 

 full-grown animal. The left leg (fig. 4k) is most similar to that of the female, but less slender; the Ri 

 is represented by a conical protuberance, and a minute Se is found in Re. The right leg possesses an 

 exopodite very similar to that of the left leg, and a fairly long and slender endopodite with a slender 

 terminal bristle. Brady gives (PI. VIII, fig. 10) in his description of Rh. gigas, without having under- 

 stood its real nature, a figure of the fifth pair of legs in the young male; the Ri dext. has two bristles 

 in stead of a single one, and the Se of Re is missing; in the former feature a valuable character between 

 the yo* of the two species is probably found; the latter character is probably due to a mistake (or an 

 abnormity) as an exterior seta is present even in the mature female of Brady's species (PI. VIII fig. 9) 

 as well as in Rh. grandis Giesbr. in contrast to the female of Rh. nasutus. 



Y. . J* (St. IV). Size: 3-9 mm. This stage is characterized by the three somites of the urosome. 

 The pes V is better developed in the male; the right and the left legs are as shown in fig. 4! nearly 

 symmetric. The Ri sin. is longer than in the preceding stage, but shorter than the Ri dext, which is 

 however shorter than the Re dext 



Variation. A mature female (Thor St. 72; fig. 4b) had the lateral thoracic spine on right side 

 of fourth thoracic somite distinctly bifurcate (in the same specimen a nematode was dwelling as para- 

 site); a corresponding variation was found in a specimen from Thor St. 183, but in addition the right 

 dorsal spine of the first abdominal somite was bifurcate. In a mature female from Thor St. 82 the 

 latter abnormity was found on both sides and in a young female on the left side only. In a single 

 specimen (Thor St 88) the Re of the right fifth foot has a lateral pointed projection (fig. 4d); about 

 the variations in the fifth pair of legs in the males I refer to the description of the male. 



