222 PROFESSOR CHARLES CHILTON ON THE 



either the Saldanha Bay or the South Orkneys specimens before me, and these, as 1 

 have said, must, I think, be referred to P. antarctica. 



STEERING, in 1906, made P. osborni Caiman a synonym of P. tenuipes Haswell, to 

 which he also assigned P. obtusa G. M. Thomson and, with a " ? ", P. brevicornis 

 Haswell. 



In describing P. osborni, CALMAN referred to the southern species described, and 

 said they " are probably all referable to one." If this is done, however, it will then 

 certainly be impossible to retain his species as distinct. This will be seen if we take 

 the points of difference in order : 



1. Dorsal processes of urus much less prominent. This applies also to the South 

 Orkneys specimens, and, to a less degree, to the Saldanha Bay specimen. 



2. Maxillipeds with outer plates nearly equalling the palp in length and bearing 

 only about eleven spines. In the South Orkneys specimens the plates bear only 

 eleven spines, though they are rather shorter than the palp. In P. atolli, too, WALKER 

 describes the spines on the outer plate as few in number and present on the distal 

 portion of the margin only. 



3. Propod of first gnathopod with palmar edge short and not more than one-third 

 the length of the dactyl. In the Saldanha Bay specimen the gnathopod agrees well 

 with CALMAN'S description, except that the palm is perhaps a little longer. From the 

 appearance of this specimen, however, I think the palm is really longer than is shown 

 in CALMAN'S figure, and that the lobe against which the dactyl is represented as 

 impinging is overlapped by the dactyl folding in on one side of it. If this is so, there 

 is no essential difference between the palm of P. osborni and that of P. antarctica 

 as figured by STEBBING under the name P. kergueleni. 



CALMAN'S description of the second gnathopod agrees quite well with that of the 

 Saldanha Bay specimen. 



4. Fourth side plate having the anterior process reduced to a short, blunt lobe. 

 This applies also to the Saldanha Bay specimen and to P. atolli Walker. 



5. Propod of third perasopod not widening distally. Both the Saldanha Bay and 

 the South Orkneys specimens agree in this point with CALMAN'S figure rather than with 

 STEBBING'S ; the difference is one of degree only, arid the widening is probably more 

 marked in older specimens. 



In view of all the considerations mentioned above, I feel compelled to unite also 

 P. atolli AValker, from the Male Atoll, Maldive Archipelago, with P. antarctica. 

 His description of the gnathopoda and of the first and second perseopoda, and of the 

 side plates corresponding to these appendages, applies very well indeed to the Saldanha 

 Bay specimen and also fairly well to P. osborni ; but in the fewer spines and teeth on 

 the outer plate of the maxillipeds and on the uropoda, P. atolli agrees rather with the 

 South Orkneys specimens. Its chief peculiarity seems to be the fact that the palp of 

 the first maxilla has " the top squarely truncate and crowned with short teeth," but in 

 view of the other characters this is hardly sufficient to maintain it as a separate species. 



(ROY. soc. EHIN. TRANS., VOL. XLVIII., r>01.) 



