562 CLARK: GEOGRAPHICAL RANGE IN RECENT CRINOIDES 



part are known to within a comparatively small limit of error, 

 with the geographical ranges calculated as the sum of the units 

 measuring 15° on each side within which they occur, though 

 apparently perfectly logical, at the present state of our knowl- 

 edge is not practicable, and cannot give results of value. 



If we assume that the Malayan region is the center of distribu- 

 tion of the recent crinoids, a very simple way of expressing the 

 comparative potential geographical range of the several crinoid 

 types becomes possible. If we multiply the number of units of 

 15° between the meridians bounding the region inhabited by each 

 type by the number of units of 15° between the parallels of 

 latitude bounding the same regions, always reckoning east and 

 west and north and south from the Malayan region, we will 

 obtain for all types (excepting only the Holopodida? which, 

 alone among the crinoid families, does not occur in the Malayan 

 region) strictly comparable areas expressed in units of 15° on 

 each side, that is, including 225 "square" degrees each. 



The geographical ranges of the families of recent crinoids ex- 

 pressed in these units are: 



Capillasterinee 30 



Comactiniinse 30 



Comasterinae 12 



Zygometrida} 6 



HimerometridiB 10 



Stephanometridse 9 



Mariametridae 12 



Colobometridae 20 



Tropiometridse 19 



Calometridaj 5 



Ptilometrinae 5 



Thalassometrinse 24 



Charitometridse 20 



Antedonina; 18 



X 6 

 X 6 

 X 6 



X 

 X 

 X 



5 

 5 



4 



X 6 = 



X 6 = 



X 6 = 



X 6 = 



X 5 = 



X 8 = 



X 6 = 



X 6 = 



180 Thysanometrina; 18 X 4 = 72 



180 Zenometrina? 24 X 10 = 240 



72 Perometrina; 17 X 4 = 68 



30 Heliometrinse 24 X 12 = 288 



50 Bathymetrina) 24 X 10 = 240 



36 Pentametrocrinida? 16 X 10 = 160 



72 Atelecrinida; 20 X 3 = 60 



120 Pentacrinitida 20 X 6 = 120 



114 Apiocrinida; IX 2= 2 



30 Phrynocrinidaj 6X 2 = 12 



25 Bourgueticrinidffi 16 X 10 = 160 



192 Holopodida; 2X 2= 4 



120 Plicatocrinida? 24 X 9 = 216 



108 



On the accompanying diagram (fig. 2) are shown the maximum 

 bathymetric range of each family of recent crinoids (in a dotted 

 line) and the geographical range calculated according to the 

 method just described (in ah unbroken line). 



The correspondence between the bathymetric range and the 

 geographical range as thus calculated is very striking, bringing 



