PANAMIC AND WEST INDIAN ECHINID FAUNA. 221 



on both sides of the Atlantic or Pacific. The causes now at work appear 

 sufficient to explain their relationship, when we take into account what 

 is known of the efficient transporting agency of equatoHal or other oceanic 

 currents for the pluteus or the young stages of Echini during a considerable 

 period of their post-embryonic life. We should also remember that, even 

 with our imperfect knowledge of the bathymetrical range of Echini, the 

 range in depth of many genera is known to be very great, as will be seen 

 from an examination of the lists given in the " Challenger " Eeport and 

 from the depths obtained by this Expedition. Among them I may mention 

 those having a wide geographical distribution as well as a great bathymet- 

 rical range.^ Tliis will serve to show the extent to which many species 

 can slowly migrate upon the bottom, even at a very considerable distance 

 from land or continental or insular slopes, when living in the track of a 

 great equatorial current wdiich brings them a constant and abundant supply 

 of food. 



Doederlein^ has also called attention to the extensive geographical dis- 

 tribution of many species of Echini in the Indo-Pacific realm,^ — a huge 

 realm extending from the Red Sea to the Sandwich Islands and from the 

 Paumotus to Mozambique; so that it is natural to expect to find local varie- 

 ties due to the limited migration of many of the species, in spite of the 

 extensive migration of others during their pluteus existence. He enumerates 

 the Red Sea, Western India with the east coast of Africa, Mauritius and 

 the Seychelles, the Indo-Malay district from New Guinea to Ceylon, and the 

 east coast of Australia as four somewhat independent realms of the great 



■ Genera. Range in fathoms. Genera. Range in fathoms. 



Dorocidaris 874 Fibularia 950 



Porocidaris 1444 Pourtalesia 2550 



Centrocidaris 1975 Homolanipas 1600 



Salenia 1850 Maretia 800 



Podocidaris 1075 Echinocardium 2675 



Coelopleurus 1323 Hemiaster 400 



Aspidodiadema 1800 Brissopsis 2435 



Dermatodiadema 800 Aerope 600 



Phormosoma 1100 Cystechinus ...... 900 



Temnechinus * GOO Pilematechiuus 1825 



Trigonocidaris 460 Urechinus 600 



Echinus 2400 Periaster 1800 



Sphaerechinus 400 Schizaster 1400 



Hipponoe 451 



2 Bericht iiber die von Henn Professor Semen bei Amboina und Thursday Island gosammeUen 



Echinoidea. Jena, 1902. Aus Semou, Zoologische Forschungsreisen in Australien und dera IMalay- 



ischen Archipel. 



* See A. Agassiz, Revision of the Echini, 1872, Plates A-G, pp. 205-212. * Genocidaris. 



