CEPHALOPODA, I. OCTOPODA 



By G. C. Robson, m.a.^ 

 (Plates III and IV, text-figs. 1-18) 



INTRODUCTION 



THE Octopoda obtained by the 'Discovery' form a rich and important collection. 

 Fifty-nine specimens were obtained, representing fourteen species. Of these the 

 majority were taken in sub-Antarctic or Antarctic waters, the collection being the 

 richest ever obtained in these latitudes. 



The series is of more than ordinary interest from the systematic and distributional 

 point of view. The chief items of interest may be presented under two heads. 



1 . The expedition obtained a number of rare pelagic Octopods belonging to various 

 families. The most important of these are a single male of a new species of 

 Vitreledonella , and one specimen each of the rare genera Alloposus and Amp/ntretus, 

 both constituting the types of new species. A new and remarkable species of Cirro- 

 teuthis was obtained, for which a separate genus may ultimately be required. 



2. Perhaps the most valuable outcome of this study is the flood of light cast on the 

 genus Eledone by the plentiful supply of specimens which were obtained by the expedi- 

 tion. No less than forty-three specimens of this characteristic Antarctic group were 

 obtained, representing four species. Two of these species are new, and for one of these 

 a new genus is created. 



The study of these forms confirms me in the belief that the Antarctic is, as Berry 

 (1917, p. 13) suggested, the metropolis of this group. It is absent from nearly the whole 

 of the Indo-Pacific and Aleutian regions, and is rather sparsely represented in North 

 Atlantic waters. 



Naef has questioned whether the genus as known to him might not be polyphyletic. 

 Study of the Discovery material and a re-examination of the types of Hoyle's ' Chal- 

 lenger' species has rendered it most probable that Naef's suggestion is correct. The 

 Mediterranean and Antarctic forms are shown to be radically dissimilar in several im- 

 portant characters, and it seems more likely that the single row of suckers (the only 

 common feature^) has been acquired independently on two or more occasions. Further- 

 more, the group of sub-Antarctic and Antarctic forms is not homogeneous. Grane- 

 ledone (represented by G. charcoti, etc.) is very distinct from Thaiimeledotie and Eledone 

 rotunda from further afield but possibly having a sub-Antarctic range. Berry's E. 

 challengeri (Kermadec Is.) (= " verrucosa^'' Hoyle, 1886) seems to require recognition in a 

 separate genus on account of its archaic radula. Thaiimeledone and Eledone rotunda both 



1 Published by permission of the Trustees of the British Museum. 



^ It is not yet certain how many species of Eledone share with E. cirrosa and moschata the charac- 

 teristic of depositing large eggs. 



