38 IOWA STUDIES IN NATURAL HISTORY 



NiDORELLiA C-^NOCENTROTUS (Galapagos 



Heliaster Islands also) 



Amphiaster Tetrapygus 



West Indies and eastern Atlantic ; Hawaiian Islands ; southern 

 Japan; Kei Islands 



C^nopedina 



Western coast of Mexico; Hawaiian Islands; Australia, Tas- 

 mania and Lord Howe Island; Mediterranean Sea and eastern 

 Atlantic 



Centrostephanus 



Southern and Lower California, southern Japan, and south- 

 ern Australia 



Heliocidaris 



West Indies and the Hawaiian Islands 



PODOCIDARIS 



West Indies and southern Australia 



Ophioprium 



Southern California and New Zealand 



Ophiopteris 



In view of the past intercommunication between the Caribbean 

 Sea and the Pacific the similarity of certain elements of the 

 Caribbean fauna and of that of the western coast of tropical 

 America is not surprising; the latter, however, includes a very 

 considerable number of genera which occur nowhere else, to- 

 gether with a few species of characteristic Indo-Malayan types, 

 such as Mithrodia, Acanthaster, Anthenea, Leiaster, Astropyga, 

 etc., which are not represented in the Caribbean Sea. 



A significantly large number of genera, including well known 

 and conspicuous littoral types, inhabit a more or less extensive 

 portion of the following anomalous range — Mediterranean Sea, 

 Caribbean Sea, southern Australia and New Zealand, southern 

 Japan, the Hawaiian Islands, and the western coast of tropical 

 America. 



This discontinuous range, though indicated by very diverse 

 types and only in part by each, nevertheless must be considered 

 a zoogeographic unit. Its outstanding feature is the fact that it 



