GEOGEAPHICAL DISTRIBUTION. 211 



representatives of genera found in the Cretaceous. A more detailed com- 

 parison than can be given here of the present faunae with the fossils of the 

 tertiary deposits, would be most interesting; but unfortunately the materials 

 thus far collected are too fragmentary, and we must await deep-sea dredgings 

 of a considerable extent of coast, before we shall have the data needed to 

 follow up the important results to be gained in this way for palaeontology 

 and geography, of which our present incomplete materials give us such an 

 interesting glimpse. 



What we know of the Tertiaries of the West Indies and Alabama, of Malta 

 and of India, shows that with the exception of the greater extension of Echi- 

 nanthus, Enpatagus, Maretia, Scutella, Pygorhynchns, the North Atlantic 

 fauna did not differ very materially from its present conditions. The same 

 may be said of the American ; while the Tertiaries of the East Indies show 

 the presence of Temnopleurus, Pleurechinus, Heliocidaris, Rumphia, Brey- 

 nia, Maretia, — genera which are still characteristic of the same districts. 



As far as we can judge from the present geographical extension of the 

 genera characteristic of the different great Marine Realms, we can only recog- 

 nize four (PL G); the American, the coasts of the two sides of this continent 

 (north and south), being characterized by Echinarachnius, Arbacia, Encope, 

 Mellita, Hemiaster. The species of this realm extend as far as the Mediter- 

 ranean and the West Coast of Africa, where they unite with the species of the 

 North Atlantic Realm, Echinus, Sphaerechinus, Schizaster, Strongylocentrotus, 

 Dorocidaris, Spatangus, Echinocyamus, Echinocardium, and extend along the 

 Japanese coast to meet the great Indo-Pacific Realm ; the Atlantic Realm 

 extending through the Red Sea, Indian Ocean, to Japan, forming a belt of 

 species, Schizaster, Sphaerechinus, Echinocardium, Spatangus, now disconnect- 

 ed from the North Atlantic Realm except by the circumpolar species, which, 

 however, does not show the former association, through the Red Sea and 

 North Africa, as well as the existence of the above-mentioned genera asso- 

 ciated with thoroughly characteristic Indo-Pacific species. We must look 

 upon the great extension of the genus Strongylocentrotus along the whole 

 of the West Coast of North and South America and of Echinocardium as indi- 

 cating a possible genetic connection between the species of the Arctic and 

 Antarctic Seas. 



The characteristic genera of the Indo-Pacific Realm are Phvllacanthus, 

 Colobocentrotus, Heterocentrotus, Paraselenia, Fibularia, Echinostrephus, 

 Laganum, Maretia. This realm is connected with the American Realm by the 



