THE CII^TOGNATHA. 



75 



forwards * as an expansion of the epidermis up to or to the middle of the ventral 

 ganglion. Tail-fia truncate. 



Jaws slender, not stron<^ly curved, the tips bent through nearly 90° into a hook f . 

 Teeth broad below : in old specimens very closely set, long, and sharp. Corona ciliata 

 not observed J. 



Distribution. — Some years ago, in a most instructive paper, Prof. Chun § discussed 

 the known occurrences of this species, and utilised them to illustrate the theory that the 

 alleged similarity between the epiplankton of subarctic and subantarctic |1 regions 

 might be explained by tbese two cold-water faunas being really continuous by way of 

 the cold deep water of the main oceans. 



According to the theory, hamata, an essentially cold-water form, should at low 

 latitudes (high upper temperatures) fail in the epiplankton, but be captured in the 

 mesoj)lankton. 



In my Taeroe Channel cruises, hamata was fairly plentiful in the epiplankton, but 

 occurred with even greater regularity in the mesoplankton ; apparently like some other 

 supposed subarctic forms, it showed even at that latitude a preference for the deep cold 

 water, water which in that area was purely of arctic origin. 



It is, therefore, very interesting to find that, even as far north as our positions during 

 the 1900 cruise, it failed altogether in hauls at the surface or 25 fathoms; it appeared 

 once only at 50 fathoms ^, twice at 75 fathoms, but regularly at deeper horizons down 

 to 2000 fathoms. 



At 



fathoms it occurred in out of 25 hauls 



50 



75 



100 



riooo"^ 



1 100 ) 

 C2000~) 

 ] to [ 

 (.lOOOJ 



22 



30 



= 73 



= 11 



This table shows clearly that Avhile odd specimens (and, as a matter of fact, tiny 

 specimens) may range exceptionally as high as 50 fathoms, it is between 2000 and 100 

 fathoms that this species is to be sought. Below 1000 fatlioms it was only captured 



* This is 80 constant in apparently perfectly preserved specimens that I have no doubt that it is a normal 

 structure. 



t This is less marked in the older (ventral) teeth of old specimens, probably the result of wear. 



t Figured by Strodtman, Arch. Naturgeschichte, 1892, pi. xvii. fig. 18. 



§ C. Chun, ' BeziehuDgen zwischen dem arktischcn und antarktischen Plankton,' Stuttgart, 1897. 



II In the discussion of this alleged " Eipolarity," the issue has been obscured to some extent by loosely terming 

 the regions under discussion "arctic" (Labrador, Cireeuland, Iceland, N. Norway, ifec.) and "antarctic" (Patagonia, 

 S. Georgia, the Kerguelen area, &c.). These regions are more correctly classed by temperature as subarctic and 

 subantarctic : between the faunas of truly arctic and antarctic regions, with a permanent sea temperature of 0'' C. or 

 thereabouts, no real resemblance has been shown. 



^ This haul, 25 «, is under suspicion : it may be a portion of 25 d, 100 to 0. 



>&^^^r- 



