PYCNOGONIDA— CALMAN. 



IV.-NOTES ON OCCURRENCE AND DISTRIBUTION. 



Prof. Bouvier has remarked (1913, p. 18) on the growing preponderance of the 

 Antarctic pycnogonidan fauna, as revealed by successive expeditions, over that of 

 the Arctic regions, hitherto regarded as the special headquarters of the group. He 

 states the number of Arctic and Antarctic species as 62 and 82 respectively. While 

 these numbers may be subject to some modification according to the limits assigned 

 to the geographical areas on the one hand, and to the specific groups on the other, it 

 is at least clear that, with some 14 species to be added to the Antarctic list from the 

 " Gauss" collection and 11 here described, the Antarctic seas are already known to be 

 far richer in species of Pycnogonida than any similar area of the oceans. 



As regards the numbers of individual specimens, it is to be noted that, out 

 of a total of about 600 in the present collection, no fewer than 240 belong to a 

 single species, Nymplion australe, and that, of these, 200 were obtained at a single 

 station, and presumably at a single haul of the trawl. Again, the three closely allied 

 species of Achelia (which are, perhaps, not more than forms of a single species) are 

 together represented by more than a hundred specimens, of which all except three 

 were taken together at a single station. Twenty-four species were obtained only at a 

 single station each, and mostly in very small numbers. Against this we have 

 Ammothea glacialis from nine stations (25 specimens), Nymphon mendosum. from 

 eight (37 specimens), and Colossendeis frigida and Pentanymphon antarcticum each 

 from seven stations (16 and 38 specimens respectively). 



The depths at which Pycnogonida were obtained range from 11 to 300 fathoms. 

 Within these limits there are no clear indications of any marked change in the fauna. 



The high proportion of new species that Antarctic collections continue to yield, 

 and the large number of species that are known only from one or a few occurrences, 

 show that our knowledge of the Pycnogonid fauna of this region is still a very long 

 way from approaching completeness. While it would be useless, for this reason, to 

 attempt a detailed analysis of the distribution of the various species within the area, or 

 of their relations to other species outside it, the following facts seem deserving of 

 attention. Of the 48 species of Pycnogonida obtained from the Ross Sea area (off the 

 coasts of Victoria Land) by the "Southern Cross" (Hodgson, 1902), "Discovery" 

 (Hodgson, 1907), and " Terra Nova" expeditions, 15 are on the list of the " Gauss" 

 (Hodgson, 1914-15) from Wilhelm Land, and 17 were obtained in the region of Graham 

 Land (including the South Orkneys and South Shetlands) by the French (Bouvier, 

 1907 and 1913) and Scottish (Hodgson, 1908) expeditions. Five species are common 

 to all three regions, and for these, at all events, a circumpolar distribution may be 

 taken as proved, while it is at least highly probable in the cases of the other 12 species 

 common to Graham Land and Victoria Land, and of the one {Austropallene cristata 

 (Bouvier)) recorded from Graham Land and Wilhelm Land only. On the other hand, 



