560 CLARK: GEOGRAPHICAL RANGE IN RECENT CRINOIDES 



Plotting these together with the maximum range for each family 

 (fig. 1), we notice very little similarity between the two lines. 

 It is interesting to observe, however, that in the left half of the 

 diagram,^ including all of the better known families, the agree- 

 ment between the geographical and the bathymetrical ranges 



Fig. 1. Comparison between the maximum bathymetric range (....) 

 and the geographical range, expressed as the sum of the areas of 15° on each 

 side within which the families occur ( ). 



is somewhat closer than in the right half, which includes the rarer 

 types. 



There is a very grave source of error in comparing the geo- 

 graphical and the bathymetrical ranges of any animal group by 

 this method, and that is that single observations are always of far 



