220 PANAMIC DEEP SEA ECHINI. 



We can well imagine an equatorial current during Miocene and Eocene 

 periods taking the .young of the Echini flourishing in the Crag, and in the 

 Mediterranean, and in the southern extension of that fauna perhaps as far 

 as the Cape Verde Islands, and bringing them to the shores of northern 

 South America or into the Caribean Sea. That stretch is but little longer 

 than the stretch which we know to be annually traversed by Acalephs, 

 Pteropods, Fishes, ami Annelids along the course of the Gulf Stream from 

 the Straits of Florida to Narragansett Bay, and to the southern shores of 

 Cape Cod and the adjacent islands. 



In discussing the relations of the West Indian and Mediterranean Echinoid 

 faunas Gregory maintains that a shallow water connection is essential. 

 There are a number of species of recent Echini which are common to the 

 Mediterranean and West Indies, and which have not worked their way from 

 one area to the other round the northern shallow water connection of the 

 present day or those of a mid-atlantic land of a former period. They are 

 found in deep water, have a wide geographical distribution, and, though 

 some of them have pelagic plutei, others have not, and are viviparous. 

 While the " Challenger," as is stated by Gregory, 1 did not collect any 

 plutei, yet there have been many Echinid and Actinid plutei collected by 

 other expeditions at a great distance from land. 



As regards the statement that Temnechinus was " probably viviparous," 

 we know nothing on the subject, and there is no proof that either S. Park- 

 insoni or S. Scilke were viviparous. The number of recent Echini which are 

 known to be viviparous is not " many." There are only two Cidaridaa, 

 Hypsechinus, Anochanus, and Abatus. 2 Ludwig enumerates as viviparous 

 thirteen Holothurians, five Echinoidea, twelve Ophiurans, seventeen Star- 

 fishes, and one Crinoid, — certainly not a large percentage of viviparous 

 Echinoderms. 



The migration of Echinoderms is not limited to the range of their plutei. 

 Young Echini, Starfishes, Holothurians. and Ophiurans are to be met with 

 floating on the surface at great distances from shore, so that the young of 

 viviparous Echinoderms play an important part in extending their geo- 

 graphical range. 



The existence of a continent or of intervening islands does not seem to 

 me necessary to explain the similarity of the Echinid fauna of former times 



1 Loc. cit. p. 106. 



2 Ludwig, H., Zool. Jahrb. 1904, Suppl., VII, p. 600. 



