CLARK: RECENT CRINOID FAUNA 9 



tic. The Australian and the Indo-Pacific-Atlantic faunas over- 

 lap more or less in the Moluccas and in the Lesser Sunda Islands, 

 and at the present time the entity of the former has become 

 clouded and largely masked through the intrusion of numerous 

 alien types from the IVIalayan region, particularly on the east 

 Australian coast. The Australian fauna appears to be the last 

 remnant of a once dominant fauna which, overwhelmed by a 

 more vigorous fauna of subsequent origin, now persists only 

 in the Australian littoral, and, almost entirely submerged, in 

 the littoral and sublittoral zones of the Caribbean Sea. 



II. The Indo-Pacific-Atlantic Fauna: Primarily character- 

 istic of the region from Formosa to the Korean Straits, and 

 eastward to Tokyo Bay, the Hawaiian Islands, the Kermadec 

 Islands, the Admiralty Islands, the Meangis Islands, the Moluc- 

 cas, the Lesser Sunda Islands, thence westward and northward 

 along the southern shores of Java and Sumatra to the Nicobar 

 and Andaman Islands, Ceylon and southwestward to Madagas- 

 car and southeastern Africa, northwestern Africa and south- 

 western Europe, and the Caribbean Sea. From this primary 

 region, which falls into numerous subdivisions, faunal units, more 

 or less differentiated from the original unit, have been and are 

 being evolved (the ''derived" faunas mentioned beyond) which 

 occupy the entire area of the present seas at all depths, excepting 

 only the Australian littoral. 



The Indo-Pacific-Atlantic fauna, chiefly developed between 

 the temperature of 10° and 18°.33C. (50° and 65° Fahrenheit), 

 and composed entirely of species of moderate size, none very 

 large and none very small, appears to represent the dominant, 

 conservative, and homogeneous widely spread fauna of the more 

 recent geological past, and to be the original homogeneous unit 

 from which the recent faunal units are being evolved (1) by 

 disruption of the ancient land continuity and consequent geo- 

 graphical differentiation, (2) by migration of certain virile types 

 into the cold abysses where, becoming modified, they undergo 

 redistribution as abyssal types, and (3) by migration of other 

 virile types into the purely recent hot tropical littoral where, , 

 becoming modified, they are redistributed as a tropical littoral 

 fauna. 



