Manchester Memoirs, Vol. xlv. (1901), No. 14. 7 



" but now separated by Giesbrecht as a distinct species. 

 " Besides being of a uniformly larger size than C. 

 ''fininafchiais, it differs from the latter in having lateral 

 "nipple-shaped projections at the terminations to the 

 " cephalothorax, in the large square-shaped first joint of 

 "the abdomen, and in the form of the basal serratures of 

 "the 5th pair of feet." 



Even if this form be classed as a variety of C. fin- 

 viarchiais, the species cannot be called " cosmopolitan," 

 for it has not been taken within the tropical belt. The 

 close relationship between the two forms gives strong 

 evidence in favour of Murray's bipolar hypothesis, for we 

 have a single distinct species occurring in Arctic and 

 Antarctic waters, which in the warmer waters approaching 

 the tropics becomes so far modified as to form — on the 

 authority of Giesbrecht — another species. We cannot 

 consider the form inhabiting warmer waters to be the one 

 from which the form occurring in Arctic and Antarctic 

 waters has been derived, for, although modification might 

 proceed on parallel lines in a form so widely separated, 

 when subjected to similar conditions of temperature, etc., 

 yet we could not expect it to lead to an identical result 

 in the two cases. 



' " In a paper on the mutual relations of Arctic and 

 Antarctic faunas, Pfeffer, ('99 and :oi) maintains that the 

 relationship between extra-tropical forms is confirmed by 

 palaeontological evidence. 



Of the fauna of the deep sea he says : " The peopling 

 " of the deep sea from the polar zone has been an un- 

 " interrupted process from the Mesozoic age until now." 

 He holds that the migration of bipolar forms into the deep 

 waters of the temperate zone is not recent, for at the 

 present time, owing to sub-oceanic upheavals, " the polar 

 " zone in the Pacific is absolutely, and in the Atlantic 



