CLARK: GEOGRAPHICAL RANGE IN RECENT CRINOIDES 563 



our very forcibly the fact that the potential geographical range 

 of a given group is proportionate to its bathymetrical range. 



It will be noticed that, in the comparison between the bathy- 

 metrical and the geographical ranges as given on the diagram, 3000 

 fathoms in depth is the equivalent of 256 X 225, or 6400, square 



Fig. 2. Comparison between the maximum bathymetric range ( ) 



and the geographical range expressed, in units of 15° square (225 square degrees), 

 as the product of the number of degrees on the equator between the meridians 

 passing through the limits of the distribution West and East of the Malayan 

 region, times the number of degrees between the Parallels of Latitude bounding 

 the area of occurrence of the Families of Recent Crinoids ( ). 



degrees; therefore every fathom of increase in the bathymetric 

 range of a given type implies an increase of approximately 2.13 

 square degrees in the geographical range, and every increase of 



