CLARK: CORRELATION OF PHYLOGENETIC SPECIALIZATION 315 



100 fathoms, lying in a zone of higher temperature than the 

 optimum for these animals. 



Disregarding the characters under the heading ''General," 

 we see that the primitive characters are always in excess below 

 250 fathoms; this excess reaches a maximum at 550-600 fathoms, 

 slowly rising to only one-third as much at 2500-3000 fathoms. 



Including the characters under the heading "General," we 



