INTRODUCTION 63 



S. Sand. S. Ork. S. Shet. Palm. 



# 

 # 



T 



*Neactaeonina cingulata (Strebel, 1908) — 



*N. edentula (Watson, 1883) 



*Toledonia major (Hedley, 191 1) 



*Philine alata Thiele, 1912 * 



' Retusa' antarctica Melvill & Standen, 19 12 — T. 



Cleodora sulcata (Pfeffer, 1879) M. 



Limacina helicina (Phipps, 1774) M. — 



' L. costulata Preston, 1916' 



L. balea (Moeller, 1841) M. 



Clione antarctica Smith, 1902 M. 



Spongiobranchaea australis d'Orbigny, 1840 M. — 



Notaeolidia gigas Eliot, 1905 T. 



N. purpurea Eliot, 1905 T. 



Necromantes appendiculata (Eliot, 1905) Tritonia T. 



AMPHINEURA 



Terenochiton kerguelenensis (Haddon, 1886) (= pagenstecheri M. & S. 

 Martens & Pfeffer, 1886) 



Chaetopleara brucei (Iredale) Melvill & Standen, 19 12 T. 



Plaxiphora aurata (Spalowsky, 1795) — M. & S. 



Hemiarthrum setulosum Dall, 1876 M. & S. 



CEPHALOPODA 



Cirroteuthis glacialis Robson, 1930 — 



Graneledone turqueti Joubin, 1905 — SK - 



BIPOLARITY 



Early workers on the southern high-latitude molluscs noted the general similarity of the fauna to that 

 of the Arctic, but as pointed out by Smith ( 1 902 (a), p. 1 66) : ' It is a notorious fact that Mollusca from high 

 latitudes and from deep water are to a great extent devoid of bright colours. Even this prevailing dull 

 appearance of the shells from the Arctic and Antarctic areas is almost enough to suggest an imaginary 



resemblance.' 



Subsequent workers have eliminated many molluscan claims to bipolar distribution either by demon- 

 strating from anatomical researches that quite different animals are concerned, or by revealing the 

 presence of a more or less cosmopolitan distribution for species formerly thought to be restricted to 

 high latitudes. This is especially true in the Pteropoda. Nevertheless, a number of apparently genuine 

 instances of bipolarity remain for consideration. 



The term bipolarity has long been in use to indicate the presence of supposedly identical animals in 

 the higher latitudes of both hemispheres and their apparent absence from intervening temperate and 



tropical waters. 



It has been noted that whereas certain stenothermic animals are present at moderate depths only in 

 both polar regions, they achieve continuity over the warm zones by descending to the cold waters of 

 the ocean deeps. The distribution of the molluscan genus Aforia is a case in point. 



Sverdrup, Johnson & Fleming (1942) define the three hypotheses that have been advanced to explain 



bipolarity. They are : . , 



(1) ' Bipolar animals are relics of a previous cosmopolitan fauna, the tropical portion of which is now 



extinct.' 



(2) 'Animals have migrated through cold deep water.' 



(3) 'Parallel development of the bipolar forms.' 



