725 



THK UKCENT CKINOIDS OF AUSTRALIA — CLAHK. ,.681 



The genus Oligoiiietra here, from the widely spread serrij>i}ni(t 

 stock, produces an entirely distinct species, 0. carpenteri, which, 

 again, is the extreme fomi of the genus, and from a somewhat 

 dift'erent '.)rancli (from whicli 0, thetidis is also derived), 0. adeonce. 



But perhaps as significant as the occurrence of »\\ these extreme 

 forms is the absence of many genera which we are accustomed to 

 consider as an integral part of the fauna of the Indo-Pacific- 

 Japanese legion. In the Comasteridse, Comiiiia and Comissia are 

 lacking j in the Zygometridfe Eudiocrinus and Gatoploinetra are 

 not found; the families Pontiometridse and Calometridse are 

 absent; in the family Himeiometiidse we fail to tind Himero- 

 metra ; in the Mariametridse, Mariametra and Selenevitra ; in 

 the Stephanometridte, Oxymetra ; in the Colobometridse, CylJo- 

 metra ; in the Thalassometridse Asterometra or Pterometra ; in 

 ttie Antedoninse, Mastigoinetra or Iridometra ; the subfamilies 

 Perometrinse, Zenometrinse, Heliometrinse, and Thysanometricse 

 Are not represented at all, though they include seven genera 

 abundantly represented in the shallow waters of the East Indies. 



While undoubtedly further investigation will fill some of these 

 gaps, still there are so many of them that their significance cannot 

 be denied ; the rich East Indian fauna in spreading southward has 

 been modified, first l)y a selective weeding out of its component 

 genera and species, which has been in part compensated by a 

 development into extreme species of genera from other stock. 



This process has given the North Australian fauna as compared 

 with the pai'ent East Indan stock a curiously unbalanced aspect; 

 the Comasteridse and Zygometridse are over-developed to the great 

 detriment of the other groups, especially of the Macrophreata ; 

 and on the whole this change has been sufficient to entitle the 

 Australian coasts from Shark Bay and Sydney northward to 

 rank as a separate subregion of the general Indo-Pacific-Japanese 

 region which may be called the North Australian Subregioii, to 

 which the South Australian Subregion must be subordinated as a 

 daughter division. 



The North Australian Subregion is the equivalent of the 

 Japanese, the South-east African, and the North-east African 

 Subregions, and, like them, is the result of an adaptation to 

 diverse environments of a common stock, the component species 

 of which have in each case been sifted out and modified in a 

 different way. 



But there is this important difference in respect to the Crinoids 

 of the Australian Subregion as compared with the other sub- 

 regions of the great Iiido-Pacific area ; the peculiar species are 

 always differentiated by an exaggeration of the specific characters. 

 A fauna in its infancy is characterized by an enormous diversity 



