190 PROFESSOR CHARLES CHILTON ON THE 



WALKER'S figure is taken from a male specimen, and shows the long second antennae 

 found in that sex; these are longer than in the males of Orchomenopsis chilensis 

 (Heller) and some other allied species. The occurrence of some specimens with long 

 lower antennae was pointed out by PFEFFER in his original description. 



Whether it was necessary to establish the new genus Waldeckia for this species 

 appears to me to be doubtful, but as that has been done I am referring the species to it. 

 As mentioned above, STEBBING in his Tierreich Amphipoda placed the species under 

 Orchomenopsis, and the affinities of the species seem to me to be distinctly with species 

 of that genus such as 0. chilensis (Heller) and 0. nodimanus Walker. It is true that 

 CHEVREUX has described the propod of the first gnathopod of W. obesa as being simple 

 and not subchelate ; but in my specimens, although the propod narrows very considerably 

 distally, there is a distinct though short palm, and this is shown also in the figures given 

 by PFEFFER and WALKER. Moreover, there are considerable differences in the breadth of 

 the propod in other species of Orchomenopsis, as will be seen from my discussion of 

 0. chilensis (Heller) ; and in the South African specimens which I refer to that species 

 the propod narrows distally in the same way, though not to the same extent, as in 

 W. zschauii. 



The other important point in which Waldeckia differs from Orchomenopsis, as first 

 pointed out by CHEVREUX, is in the possession of finger-like accessory branchiae. 

 CHEVREUX describes one of these as being present on all the legs, and two on the fourth. 

 In the specimens I examined I found them on the fourth, fifth, and sixth legs only, and 

 only one on the fourth. They appear to arise either from or near the base of the branchia. 

 They are long and finger-like in shape, but seem to differ in internal structure from the 

 branchia, being filled with granules or globules of some kind, and whether they are really 

 branchial in function is perhaps doubtful. This, however, is neither the time nor the 

 place for a discussion of their physiological importance ; the question that concerns us 

 now is their presence or absence, and their value when present as a generic character. 



Secondary or accessory branchiae have been described in several genera of the 

 Amphipoda belonging to quite different families, and it seems probable that they may 

 be independently developed in cases where there is special need for them, and that their 

 presence is not of great taxonomic importance. For example, they occur in some species 

 of Hyalella and not in others, and the species in which they occur are nevertheless 

 retained under the genus Hyalella. It was not till after I had written down the 

 general considerations given above that I had an opportunity of specially looking for 

 accessory branchiae in other allied species ; but afterwards, on examining large specimens 

 of Orchomenopsis chilensis Heller ( = O. rossii Walker), from Station 411, whence 

 the Waldeckia zschauii had been obtained, I found them in that species also, though 

 they appear to be present only on the fifth and sixth legs. Unfortunately, my atten- 

 tion was not specially directed to this question till it was too late to make an examina- 

 tion of other specimens, but the facts detailed above show, 1 think, that Waldeckia is 

 nearer to Orchomenopsis than might appear at first sight. 



(ROY. SOC. EDIN. TRANS., VOL. XLVIII., 472.) 



