CLARK: DISTRIBUTION OF CRINOIDS 79 



resulting in an inflow of oceanic water. The biological condi- 

 tions in an inland sea are not in any way concerned with the 

 question whether the sea originated by a sinking of the land, or 

 whether it arose by a restriction of a previously much larger body 

 of water. Both processes lead to a mean which is physically 

 and oceanographically the same, and therefore biologically the 

 same. 



A number of curious types occur in enclosed seas which are 

 quite different from any types inhabiting the oceans with which 

 these enclosed seas were once connected. These types are mainly 

 to be interpreted as rehcs of a once generally distributed fauna 

 which, able to survive the changing conditions, have been pre- 

 served from extermination by the fact that none of the eco- 

 nomically more efficient types of later origin, through competi- 

 tion with which they have been extirpated from the oceans, have 

 been able to enter the enclosed basins, for the reason that these 

 basins became cut off from the oceans before the appearance of 

 these later types. 



Such types are found in enclosed seas, but almost never in in- 

 land seas, for the reason that all types of later origin are ex- 

 cluded from the former; an animal type efficient and vigorous 

 enough to overcome and to exterminate competing types in the 

 oceans would, other things being equal, also be efficient enough 

 to extirpate them from all the inland seas. 



Among the crinoids two such types occur in the Caribbean Sea, 

 Isocrinus and Holopus. These persist here not for the reason 

 that they originated here, but because the disruption of the con- 

 nection between the Caribbean region and the East Indies took 

 place before the evolution of the more efficient and vigorous types 

 now dominant in the Indo-Pacific littoral, through competition 

 with which they have there been extirpated. 



It is a curious fact that the sea about the Antarctic continent 

 is more in agreement physically, chemically and biologically with 

 an inland sea than with an ocean or broad embayment like the 

 Arabian Sea or the Bay of Bengal. It might aptly be described 

 as a combination of the Arctic Ocean and the Mediterranean, 

 that is, a chilled Mediterranean; for the temperature is low, 



