CLARK : RECENT CRINOIDS 



581 



According to the extent of their respective temperature 

 ranges (fig. 2) the famihes of recent crinoids group themselves 

 as follows: « 



1°- 6° (including families with one record only) 4 



6°-12° 1 24°-30° 4 



12°-18° 2 30°-36° 7 



18°-24° 3 36M2° 2 



Fig. 2. Distribution of the families of recent crinoids according to their ther- 

 mal ranges. 



In the comatulids (fig. 3), although the OHgophreata and the 

 Macrophreata are represented by the same number of families, 

 six, between 50° and 55°, the families of the JMacrophreata pre- 

 dominate at all temperatures below this, and the families of the 

 Oligophreata at all temperatures above; but the total number of 

 the families of the Macrophreata in excess of the total number of 

 the families of the Oligophreata occurring below 55° is only two, 

 while the total number of the families of the Oligophreata in 

 excess of the total number of the families of the Macrophreata 

 occurring above 55° is six. This indicates that the differentiation 

 of new crinoid tj^pes is chiefly, if not entirely, confined to the 

 warmer portions of the oceans. 



There is a gradual increase in the number of the families of 

 the Oligophreata from 30°-35°, where one only is represented, to 

 60°-65°, where there are six, and then a more gradual decrease 

 as the temperature increases. 



Among the families of the JNlacrophreata there is an increase, 

 at first more abrupt than in the case of the Oligophreata, from 

 25°-30°, where one family is represented, to 50°-65°, where there 

 are six, and then a decrease, at first much more abrupt than 

 among the families of the Oligophreata, as the temperature in- 

 creases. Thus in the Oligophreata we find the largest number of 



