A. H. Clark — Groups of Recent Crinoids. 



6? 



Abt. YI. — The Relation between the Maximum and the 

 Average Bathymetric Range, and the Mean and the Aver- 

 age Depth of Habitat, in the Subfamilies and Higher 

 Groups of Recent Crinoids ;* by Austin H. Clark. 



In the discussion of the bathymetric distribution of 

 the various classes of marine invertebrates relatively little 

 attention has heretofore been paid to the question of the 

 average as compared with the total bathymetric range, and to 

 the average as compared with the mean depth of habitat. Yet 

 this aspect of the study of bathymetric distribution is of the 

 greatest importance ou account of its possible bearing on prob- 

 lems connected with paleontology. 



The maximum and the average bathymetric ranges, and the 

 mean and the average depth of habitat, of the subfamilies and 

 higher groups of recent crinoids are given in the following 

 table : 



The Maximum and the Average Bathymetric Eange, and the Mean and the 

 Average Depth of Habitat, of the Subfamilies and Higher Groups of Recent 

 Crinoids. The three families marked with an asterisk (*) are monotypic. 



Mean Average 



Maximum Average depth of depth of 



Eange Eange habitat habitat 



Akticxjlata 2900 412 1450 595 



Pentaceinitid^e 2900 529 1450 408 



Comatulida .. 2900 429 1450 390 



Oligophreata 1600 167 800 118 



Comasteridae 830 153 415 96 



Capillasterinse 830 189 415 154 



Comactiniinse 288 180 144 90 



Comasteringe 140 90 70 45 



Zvgometridse 153 76 76 50 



Himerometridaj 61 33 30 22 



*Stephanometridse ... 35 35 17 17 



Mariametridae 84 45 42 26 



Colobometridae 140 45 70 32 



*Tropiometrid33 278 278 139 139 



Calometridae 333 142 166 102 



Thalassometridae 1600 402 800 . 274 



Ptilometrinae 134 54 73 53 



Thalassometrinse 1600 507 800 340 



Charitometridse 1170 464 615 423 



Macrophreata ...... 2900 691 1450 663 



Antedonidae 2900 572 1450 409 



Antedoninse 250 146 125 76 



* Published with the permission of the Secretary of the Smithsonian 

 Institution. 



