A. H. Clark — Groups of Recent Crinoids. 



73 



Stephanometridae 



17 



fathoms 



Capillasterinae 



154 



fathoms 



Hinierometridae 



22 



tt 



Thysanometrinae 



216 



« 



Mariametridae 



26 



« 



Zenometrinae 



315 



u 



Colobometridae 



32 



it 



Thalassometrinae 



340 



ti 



Comasterinae 



45 



u 



Heliometrinae 



383 



a 



Zygometridae 



50 



« 



Charitoraetridae 



423 



a 



Ptilometrinae 



53 



it 



Phrynocrinidae 



620 



it 



Holopodidae 



62 



a 



Atelecrinidae 



753 



« 



Antedoninae 



76 



it 



Apiocrinidae 



753 



it 



Comactiniinae 



90 



it 



Pentametrocrinidae 



828 



a 



Calometridse 



102 



u 



Bourgueticrinidae 



1134 



ti 



Perometrinae 



114 



(( 



Bathymetrinae 



1349 



n 



Tropiometrinae 



139 

 Ave 



it 



rage 



Plicatocrinidae 

 364 fathoms 



1378 



a 



The average depth of habitat of the contrasted groups is 



Inadunata 1378 fathoms 



Bourgueticrinidae 1134 " 



Pentacrinitida 427 " 



Macrophreata 663 " 



Articulata 



595 fathoms 



Pentacrinitidae 



408 " 



Comatulida 



390 " 



Oligophreata 



118 



and of the stalked groups : 



Pentacrinitidae 



408 



fathoms 



Pentacrinitida 



427 



it 



Apiocrinidae 



753 



u 



Phrynocrinidae 



620 



tt 



Bourgueticrinidae 



1134 



c< 



Holopodidae 



62 



u 



Plicatocrinidae 



1378 



It 



Considering the list of contrasted groups it is evident that 

 the more specialized the group the less the average depth at 

 which it is found. The same thing is shown by the list of 

 stalked groups, if we bear in mind that Holopus is a very 

 restricted and aberrant type, and that our knowledge of the 

 Apioerinidse and of the Phrynocrinidae is very limited. 



It is interesting to observe that the average range of the 

 families of recent crinoids is very nearly the same as, but 

 slightly more than, the average depth of habitat. The corre- 

 spondence of the two is strikingly brought out in the accom- 

 panying diagram (fig. 3). 



