14 ECHINODERMA OF THE INDIAN MuSEUM, PART VII. 



Antedonidae. 



Pcrometra Hijpalom.etra. 



Psalhyrometra. Zenonietra. 



Thysanotnetra. | Coccometra. 



Pentacrinit.ida>. 



Comastrocrinns. > 1 , . 



i,r i ■ ( /■iocri7ins. 



Metacrinus. S \ 



To the southward certain of the East Indian genera have extended, under- 

 going various curious clianges, forming an Antarctic fauna. This Antarctic 

 fauna has crept up the west coast of South and North America, passing into 

 deep water in the tropics, and now is found in the Bering Sea and along the 

 Pacific coasts of the Kuril Islands and of Japan, as far south as Tokyo Bay. 

 The Arctic and north Atlantic Oceans, from western Greenland and Nova 

 Scotia to northern Norway and as far east as the Kara Sea, contain a similar 

 fauna, which, curiously enough, is found also in the Okhotsk Sea, the Gulf of 

 Tartary, and along the western coast of the Sea of Japan as far south as Korea, 

 where it replaces the Antarctic fauna which is confined, in the north, to the 

 open Pacific Ocean and to the Bering Sea. 



The genera inhabiting very deep water in the Indian Ocean are, almost all 

 of them, found also under the same conditions in the Atlantic, but they do 

 not, except Bathycrinus , enter the deep cold pools such as that north of the Wyville 

 Thomson ridge. Contrary to what is found in many groups, the Atlantic species 

 always differ from those occurring in the Pacific. 



It has been mentioned that the geographic range of a genus and species 

 increases proportionately to the depth inhabited by that genus or species. 

 Not only do genera or species which extend from tlie shore line down to 200 

 fathoms or so have a raqgc much greater than those which do not extend down- 

 ward half as far, but the genera and species confined to the deeper water also 

 participate in this increased range. 



Taken as a whole the East Indian crinoid fauna mgiy be roughly divided 

 bathymetrically into (1) a Littoral, (2) an Intermediate, and (3) an Oceanic 

 section; but these different sections are not so well differentiated as is the case 

 with most bottom inhabiting marine organisms. 



The Littoral groups have the most restricted distribution, as is exemplified best 

 by the Zygometridse ; but the Capillastei'inae are in general almost as strictly 

 littoral in the East Indies , yet occur only at intermediate depths (with two littoral 

 records) in the West Indies, and the same is also true of several other groups. 



The Intermediate fauna is characterized chiefly by the families Thalasso- 

 metrida?, Charitometrida', Atelecrinida? and Pentacrinitida' ; and certain genera 

 of Bourgueticrinida\ Zenometrina and Heliometrinte ; but three species of the 

 Thalassometridiie are Uttoral, one species of the Charitometridse comes within 

 30 fathoms of the surface, one of the Pentacrinitidse within 5, and several of 

 the two antedonid subfamilies are sublittoral. Taken broadly, the Intermediate 



