CLARK: DISTRIBUTION OF CRINOIDS 



77 



representing the distribution according to depth of the genera 

 confined to the Atlantic (fig. 2). This is the more remarkable 

 when we remember that only one genus (Hathrometra) is com- 

 mon to the Atlantic and to the Antarctic, and to the Atlantic 

 and the Arctic, while in the polar seas the temperature is compar- 

 atively uniform from the surface to the bottom in contrast to 

 the Middle Atlantic where the surface temperature is very high. 

 It thus appears that essentially the same selective processes 

 have operated both in the Atlantic and in the Antarctic in weed- 



12346678 9 10 U12 



tso- 



300- 

 350' 

 400' 

 4«0' 

 500' 

 SbO-i 

 600' 

 550 

 700 

 7tO-l 

 800- 

 850- 

 900- 

 950- 

 lOCO- 

 1100- 

 1200- 

 1300- 

 1400- 

 15C0- 



leoo- 

 ncO' 



1600' 

 1900' 

 LOOO- 



usoo 



50 



100 

 150 

 200 

 250 

 300 

 360 

 400 

 450 

 5G0 

 660 

 600 

 660 

 700 

 750 

 800 

 850 

 900 

 ■950 

 ■lOOC 

 llOC- 

 ■12( 



■130d., 

 •140C 

 ■1S0( 

 •160( 



•i7ec 



-180( 



•190C- 



■200( 



■a50( 



-3001 



>> 



^ 



;■ 



S 



>-^ 



/ 



0-50 



60-100 



100-150 



160-200 



200-250 



260-300' 



300-350 



350-400 



400-450 



460-500 



500-560 



550-600 



603-660 



650-700 



700-750 



760-600 



UOO-850 



850-900 



900-950 



950-1000 



1000-1100 



1100-1200 



1200-1300 



1300-1400 



Fig. 2 

 -) and Antartic (- 



) 



Fig. 1 



Fig. 1. Bathymetricaldistributionof the Artie ( — 

 crinoids, and of the two combined ( ). 



Fig. 2. The frequency at different depths of the crinoid genera confined to 

 the Atlantic. 



ing out the less adaptable of the primarily Indo-Pacific genera; 

 but the results in each case are radically different, showing con- 

 clusively that the Atlantic could never have been populated by 

 passage from the Indian Ocean south of Africa, between Africa 

 and Antarctica. 



An inland sea, biologically speaking, is a more or less enclosed 

 body of water which, connected with an ocean, has received all 



