No. 503] ECOLOGY OF RECENT CRINOIDS 721 



bottom temperature is 40° F. or above. These warmer 

 areas are occupied by a fauna radically distinct from the 

 arctic fauna of the cold areas, though the depth is about 

 the same, and we find in them crinoids belonging to the 

 purely Pacific genera Thaumatometra and Psathyrometra. 

 It is gratifying to note that the representatives of both 

 these genera are far larger here than anywhere else, the 

 difference, in fact, being relatively greater than in the case 

 of Heliometra. These three genera here live among en- 

 tirely different surroundings, and in widely different 

 temperatures; but their food supply, coming in a rain 

 from above, is the same, and is, moreover, the only com- 

 mon ecological factor; therefore, there is no room for 

 doubt that the food supply is the cause of the great in- 

 crease in size. 



While the recent pentacrinites as a rule live below 100 

 fathoms, in certain places, such as in some localities 

 along the northern coasts of Cuba and Guadeloupe, and 

 in Suruga Gulf and Sagami Bay, Japan, they approach 

 much nearer the surface, and have even been taken in 

 water of between 20 and 30 fathoms (Guadeloupe). Xow 

 Cuba and Guadeloupe are mountainous islands, while 

 Suruga Gulf and Sagami Bay are close to that magnifi- 

 cent mountain Fuji-Yama, and to other high lands as 

 well. The result is that many intermittent streams flow 

 into the sea at these places, having their origin in the high 

 lands; the rise in volume of their waters is so sudden 

 that the pelagic life can not give way before it, but is 

 killed and precipitated. The greatly increased food sup- 

 ply in the vicinity of one of these streams thus brings the 

 food intensity up to such a level that the large pen- 

 tacrinites may exist in such localities in much shallower 

 water than would otherwise be possible. The water from 

 these streams is never very great in amount, and does 

 not penetrate deeply, but spreads out over the surface of 

 the sea; thus a crinoid could exist very near the surface 

 without being affected by it. Large rivers with a com- 

 paratively steady flow, on the other hand, freshen the 



