726 



682 " THETIS " SCIENTIFIC RESL'LTS. 



among the individuals of all the component species, such a state- 

 of affairs as we find to-day in the Behring 8ea ; at maturity we 

 find that the fauna has crystallized into definite fixed and stable 

 (usually new) species, some of which generally indicate new 

 generic types showing obvious relationships with the genera of 

 other regions, in senescence there occurs what has aptly been 

 termed an " explosion " of specific characters which is more or 

 less general among the component species regardless of the 

 groups to which they may belong, and may result in the sudden 

 origin of erratic generic types. Speaking in terms of faunisiic 

 ontogeny, the Crinoid fauna of Australia is a Crinoid fauna in 

 senescence, the oldest Crinoid fauna to he found in the recent 

 seas. It came originally from the northward, from the region of 

 the great East India islands ; but the fauna of these islands has 

 been at various times rejuvenated, probably through geological 

 processes resulting in changes in the land and water distribution, 

 while that of Australia has been allowed to pass peacefully into 

 old age. The past Euroiiean fauna (or more exactly that part of 

 it which is comparable to th<i existing faunas) was senescent, like 

 the present fauna of Australia ; the fauna of Eastern Africa is 

 approximately at maturity ; that of the West Indies and the 

 north-western coast of Africa is young, not having reached 

 maturity, while that of southern Japan is younger still. The 

 Arctic Crinoids indicate a fauna at maturity, composed of 

 definite fixed types; but the Antai'ctic fauna is not so old, and 

 the Antarctic extension northward to the Behring Sea presents,, 

 at least north of the tropics, all the evidences of youth. 



One cannot consider the recent Crinoids of Australia witliout 

 speculating upon the possible evidence afforded in regard to th& 

 past distribution of land and sea. It is not the place here ta 

 enter into a detailed discussion of the East Indian and Indian 

 Ocean Crinoid fauna, but a study of that fauna brings out many 

 points of the greatest interest to the Paleeontologist. What waa 

 essentially the North Australian fauna existed in Europe ; it 

 reached Europe by passage from the northern part of the Bay of 

 Bengal north of what is now India. Geological changes ha^e 

 turned the sea between the Bay of Bengal and the Atlantic into 

 land, resulting in the extirpation of all but two of the genera, 

 Antedon and Leptornetra, which have been able to survive, and 

 flourish to-day on the east Atlantic shores and the Mediterranean, 

 the only living survivors of the rich fauna that reached Europe 

 by the ancient inland sea. It is most extraordinary that these 

 two genera should have undergone so little change as to make 

 them barel}' separable from the far distant Mastigometra and 

 Psathyrovietra from which they have been derived. 



At the time when the various tropical Australian gener* 

 reached Europe, other genera, more hardy, pushed northward 



