Clark: geographical range in recent crinoides 559 



others, with a much more restricted geographical range, have 

 been reported from all points within a very large area. 



The second method first of all calls for the determination of 

 some restricted region as the center of distribution, for^it makes 

 considerable difference in calculating the potential geographical 

 range of a group like the Thysanometrina?, occurring from 

 southern Japan southward to the Admiralty Islands, and again 

 in the Caribbean Sea, whether we assume the center of distri- 

 bution to be the Malayan region, and therefore that the con- 

 nection between the two localities is westw^ard from the line be- 

 tween southern Japan and the Admiralty Islands, or whether 

 we assume some othei' center of distribution, and a connection 

 eastward through Oceania and over Central America. 



I have elsewhere- given my reasons for considering the Malayan 

 region as the center of distribution for the recent (and later 

 fossil) crinoids, explaining the similaritj^ between the fauna of 

 southern Japan and Hawaii and the Caribbean Islands as the 

 result of their present similar isolation from the Malayan region, 

 an isolation which has permitted the persistence on the periphery 

 of the area inhabited by the crinoids as a whole of types which 

 in all the intermediate regions have been extirpated by more 

 efficient competitors of subsequent origin. 



If we divide the map of the world into areas measuring 15° on 

 each side, we find that the number of such divisions covering 

 the geographic ranges of each of the families of recent crinoids 

 is as follows: 



Capillasteringe 42 Thysanometrinse 5 



Comactiniinae 28 Zenometrinse 19 



Comasterinse 30 Perometrinse -. 12 



Zygometrida; 12 Heliometrinaj 68 



Himerometrida? 22 Bathymetrina; 12 



Stephanometrida^ 14 Pentametrocrinidae 13 



Mariametridaj 30 Atelecrinida; 7 



Colobometridaj 31 Pentacrinitida 20 



Tropiometrida; 33 Apiocrinidse 2 



Calometrida; 10 PhrjTiocrinida? 2 



Ptilometrinse 10 Bourgueticrinida> 20 



Thalassometrina; 36 Holopodida? 2 



Charitometrida> 18 Plicatocrinidse 14 



Antedonina; 43 



2 Internationale Revue der gesamten Hydrobiologie und Hydrographie, Bd. 6, 

 Heft 1, S. 24. 



