CEUSTACEA OF NEW ZEALAND. 225 



anterior margin with a small tuft at the base of the dactylos and a single seta situated 

 more proximally. The dactylos is short. 



The second perceopod is exactly similar to the first in size and form. 

 The third, fourth, and fifth perceopoda are all similar to each other, but each is 

 slightly larger than the preceding ; they are all somewhat remarkable in having the 

 basos rather narrow and not expanded posteriorly into a semicircular plate as in most 

 Amphipoda. Eig. 23 represents the fourth peraeopod, and it will be convenient to 

 take this one for description, as it represents a mean between the fifth and seventh. 

 The coxa is almost semicircular, upper margin straight, the lower convex margin 

 thickly fringed with short spines, which are most numerous posteriorly. The basos 

 is narrowed a little at the base ; it is oblong, the breadth being sliglitly more than 

 one-third the length; anterior margin with two setae, one at the extremity and one 

 above it; posterior margin straight, with two or three stout setse about the middle 

 and one or two longer ones at the extremity. The ischium is very similar to that 

 of the preceding perseopoda ; the meros oblong, about three times as long as broad, 

 both margins bearing stout seta?, especially at the extremity; the carpus slightly 

 longer than the meros, but a little narrower, the setoe on it more numerous and laro-er 

 than in the meros; the propodos as long as the carpus, but narrower, apparently 

 twisted so that the dactylos projects backwards, both margins having stout seta? or spines, 

 those on the posterior margin being most numerous ; the dactylos is short, not much 

 longer than the setae at the end of the propodos. 



Hhe pleopoda (figs. 24, 25, 26) are small and are very remarkable, in that each bears 

 only one branch, wliich appears to be the outer one, there being no trace whatever of 

 the second branch. I do not know of any other species of the Amphipoda where this 

 is the case : in the Cerapiixe the inner branches may be rudimentary and even entirely 

 absent in the case of the third pleopod ; but it is easy to see that this is due to the 

 habit of the animal living in a tube, which has to some extent modified all its 

 pleopoda and the tail-part. In. the present species the portions of the j^leopoda that 

 are present appear quite perfect, and I know of nothhig in the Juibits of the animal 

 to explain why these pleopoda should have only one branch while those of Gammarus 

 fragilis and CalUopius sitbterraiieus have the normal two branches. 



The first pleopod (fig. 2i) is the longest ; the basal portion is oblong, slender, 

 without seta), except the two " coupling spines " at the extremity of the inner margin • 

 these seem not unlike those of Niphargus, each bearing two or three tubercles on the 

 one side and being slightly hooked at the end. The single branch is nearly twice as 

 long as the peduncle and consists of eleven joints, each bearing the two long plumose 

 sette in the usual way. I cannot find any trace of the " cleft spines " mentioned by 

 Stcbbing [108, p. xiv &c.], Sars [91, p. 53J, Humbert [62, p. 351], Sec, on the inner 

 margin of the first joint of this brancli, and it is therefore probable that it represents the 

 outer branch, the inner one being absent. 



Stebbing [108, p. xiv] has drawn special attention to these " cleft-spines " and also 

 to the "coupling-spines," and, with regard to the latter, points out that they have been 

 described and figured by Sars in his accoimt of Gammarus neglectus [91, p. 53], and 



