12 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



originally carried along with them, have died out. The difference in 

 depth of habitat between the species on the opposite coasts of the 

 Atlantic is probably due to a difference in the nature of the food 

 supply, and the increased depth of the habitat of the West Indian 

 genera over their East Indian relatives originated probably from the 

 same cause. 1 



There is, therefore, a close similarity in origin between the species 

 of the European and the south European-northwest African- Antillean 

 faunal divisions; the former have reached their present habitat by 

 passing northwestward around or across the northern end of what is 

 now Africa, the latter by passing more to the southward. At first 

 similar extensions from the common parent region, the diverse con- 

 ditions which in past geologic ages they encountered, one in the north 

 and the other in the south, reduced them differently, so that now 

 they present a totally different aspect, and one would never suspect 

 a common origin were they not both equally closely related to the 

 parent region. 



It is very interesting that in the ages since the constituent elements 

 of these two faunal divisions left the parent region only comparatively 

 slight changes have occurred; no widely diverse generic types have 

 been evolved, and none of the collateral parent genera have entirely 

 died out behind them, though they have largely disappeared from 

 the intervening seas of the present day, being preserved, however, in 

 certain cases, as fossils in the later rocks. 



West coast. — There are only two littoral comatulids known from 

 the west African coast and the outlying islands; one of these (Tropi- 

 ometra *picta) is, so far as I can see, identical with the commonest 

 species on the opposite coast of South America, while the other 

 (Antedon liupferi) is very close to a corresponding species originally 

 described from Rio de Janeiro and since reported from Abrolhos 

 and Madeira (Antedon diibenii). The third littoral Brazilian comat- 

 ulid (Nemaster lineata) has probably spread southward from the 

 West Indies just as Tropiometra picta has worked its way northward 

 to those islands. 



The faunal division characterized by the presence of Tropiometra 

 picta and the small short armed species of Antedon may be conveniently 

 known as the West African-South American area. 



In the deep waters of the Atlantic there occur certain genera of 

 the Oceanic region which are found in all deep seas, except that they 

 never intrude upon the territory occupied by the so-called Polar- 

 Pacific species. Such genera are Bathycrinus, Bathymetra, Orota- 

 lometra, and Thalassometra; possibly Gephyrocrinus should also be 

 placed here. 



i Geographical Journal, vol. 32, No. 6, p. G02 et seq. 



