126 SHALLOW WATER AND DEEP SEA ARCTURUS. [CH. Ill 



shallow and deep water — a very rare exception so far as 

 this group is concerned. The purely deep sea forms with 

 their habitats are the following : — 



A. glacialis, Antarctic. 



A. spinosus, Antarctic. 



A. anna, Antarctic. 



A. brimneus, Antarctic. 



A. my ops, Antarctic. 



A. cornutus, Indian Archipelago. 



A. spinifrons, Fiji. 



A. purpureus, West Indies. 



A. abyssicola, Society Islands and Cape York. 



A. tuberosus, Arctic. 



A. hystrix, Arctic. 



The facts at our disposal about the distribution of this 

 family appear to indicate that the genus Arcturus is 

 typically a deep sea genus; there are twelve deep sea 

 species as against seven shallow water forms, one being 

 common to both coasts and sea of great depth. The 

 shallow water forms are with one exception exclusively 

 antarctic in range ; while in the closely allied genus 

 Astacilla the converse is the case, there being but one 

 antarctic species. The facts look very much as if range 

 here were more a question of temperature than anything 

 else; the intervening hotter parts of the oceans are 

 without Arcturi ; but the southern forms have been able 

 to reach the northern hemisphere or vice versa by taking 

 a long dive and coming up again above the equator. The 

 deep sea in fact is a cool pathway along which Crustaceans 



