218 CLARK: DISTRIBUTION OF UNSTALKED CRINOIDS 



Japanese coasts it is interesting to note that the species of each 

 of these units show the same hne that the corresponding species 

 of the same units show in other parts of the world. The min- 

 gling of the faunas here, as elsewhere, has resulted in a distinctive 

 collection of individuals which, however, is easily resolved into 

 the original component units, and these component units are 

 found to retain all the distinctive features of the parent faunal 

 groups from which they were originally derived. In their re- 

 lation to temperature the three faunal groups are very different. 

 The Malayan species, which are mostly confined to the littoral, 

 almost all occur in water with a temperature above 23°, but they 

 are also represented between 12°, and 16°, and 2° and 7°. The 

 Indo-Pacific species have their maximum between 10° and 18°, 

 and especially between 13° and 14°; they are also numerous 

 between 5° and 6°. The Arctic and Antarctic types, which do 

 not occur in water warmer than 15°, are most numerous between 

 0° and 2°. 



We get, therefore, the following optimum temperatures for 

 these three components of the Japanese and Chinese fauna: 



Malayan 23 + ° 12°-16° 2°-7° 



Indo-Pacific 23 + ° 13°-14° 5°-6° 



Arctic and Antarctic . . . 0°-2° 



The point 2° to 7° (including 5° to 6°) is characterized especi- 

 ally by the genera of Oligophreata with highly developed side- 

 and covering-plates along the ambulacra of the pinnules and arms 

 (included in the families Thalassometridse and Charitometridse) 

 which, occurring from to 1600 fathoms, are most noticeable 

 between 350 and 400 fathoms; most of these belong to the Indo- 

 Pacific fauna, but a few are Malayan. 



Although on the Japanese coast it is possible to take species 

 of the Indo-Pacific and the Antarctic, and of the Indo-Pacific 

 and Malayan, faunal units in one and the same dredge haul, 

 it is evident that this overlapping, which in some places is quite 

 extensive, does not mean that these faunal units here have lost 

 or are losing their identity. 



