32 . "TERRA NOVA ' EXPEDITION. 



Arctic. The reasoning is therefore at fault if Brady had " species " in his mind. 

 If however " number of specimens " was intended we may perhaps agree, as, with 

 certain exceptions (Clavidina communis, CasskluUna (various species), Bidimina 

 chapmaiii, Ehrenberghia hystrix var. glabra, etc.) the Textulariidae occur very 

 sparingly hi our Antarctic material. The genus Textularia itself is represented 

 in our list by a single deep-water form, Textularia concava var. heterostoma, 

 Forn., as against three species in Brady's Antarctic list and two in his Arctic 

 list ; and other genera, where represented at all, are usually very rare. But we 

 have some forty-seven species and varieties of Textulariidae on our list, south of 

 the Antarctic Circle, so Brady's conclusion must not be accepted without further 

 evidence. As regards (b) we have already stated the reasons for our disagreement 

 with Brady's conclusion. 



As regards (c) Brady lists eight species of Nonionina, all of which figure 

 in the Arctic fauna, but only four of them appear in his Antarctic list, and 

 these are confined to the Patagonian localities and do not figure in the Kerguelen, 

 Heard Island or Southern Ocean material. Our experience is very different, for 

 we have eight species on our Antarctic list and one of them is Nonionina 

 stelligcra, d'Orb., which is one of the most characteristic Northern forms. It 

 figures in all the Arctic Stations of Brady, but at only one Southern Station, off 

 the Patagonian coast. 



Hence we may regard this conclusion of Brady's to be unfounded also. 

 Brady's tables include fifty-three genera and 189 species, of which forty-four 

 genera, represented by 137 species, occur in the Southern area and forty-one 

 genera, represented by 111 species, occur in the Northern area ; thirty- two genera, 

 represented by sixty species, being common to both areas. 



Such a large proportion of forms common to Northern and Southern waters 

 might be used as evidence in favour of the theory of bipolarity by a zoologist 

 unfamiliar with the group, but to the rhizopodist the presence or absence of a 

 few particular species would be more convincing evidence than the longest list 

 of other forms. This, for the reason that, apart from those genera and species 

 limited in their distribution by conditions of mean temperature (which form 

 the characteristic shallow water foraminiferal faunas of different latitudes), the 

 mean temperature at all depths below 500 fathoms all over the world does not 

 vary more than a few degrees, and so would constitute no barrier to the gradual 

 migration of Foraminifera from one j^ole to the other l)y way of the cold waters 

 of the deep sea. Hence we should be loth to accept the existence of any species 

 or nmnber of species in both Arctic and Antarctic waters as evidence in favour 

 of bipolarity, but should be prepared to regard the absence from either region of 

 a species hnown to be peculiarly characteristic of the other region as definite evidence 

 opposed to the theory. 



Brady's list of Arctic Foraminifera contains at least three species peculiar to 



