.1. W. GREGORY — RELATIONS OF ECHINOID FAUNAS. 101 



The following paper was then read : 



THE RELATIONS OF THF AMERICAN AND EUROPEAN ECHINOID FAUNAS. 

 liV .). W. GREGORY, F. (1. S., F. Z. S., OF THE BRITISH MUSEUM OF NATURAL HISTORY. 



( 'ontents. 



Introduction page LOI 



The Carboniferous Faunas 102 



Permian-Jurassic Faunas 103 



The Cretaceous Faunas 103 



Eocene and < Higocene Faunas I'll 



The Miocene Faunas 105 



The Pliocene Faunas 107 



Summary of Conclusions 108 



Introduction. 



Probably every paleontologisl who lives on the western border of the great 

 ••alruivtic province occasionally chafes against the limitation which the Atlantic 

 places upon our knowledge of the origin or derivation of successive fossil faunas. 

 In many cases researches on the paleontology of central and eastern Europe have 

 given the desired infbrmati< m as to the < irigin of a British or western European fauna ; 

 but in other case.- groups of genera and species appear suddenly in a certain zone 

 and as suddenly disappear. The probabilities in such cases are in favor of the mi- 

 gration of these forms from some western area. If the species in question possessei I 

 a great range, either in depth or of latitude, they present no especial difficulty ; if 

 their bathymetrical distribution was or appears to have been great, they may have 

 come directly eastward ; if they were spread over a wide area or were boreal forms, 

 they may have worked their way around the shallow waters of the northern margins 

 of the Atlantic. But there are cases that cannot be thus easily explained. The 

 genera in question may be shallow water and tropical forms to which the deep and 

 cold abysses of the Atlantic would present as insuperable an obstacle as an actual 

 land harrier. If, as seems most probable, these forms did come from the west, how 

 did they cross such a barrier, or was it in existence at that time? To solve the 

 difficulties presented by such cases, many geologists have sought to give a scientific 

 basis to the legends of the fabled Atlantis, and have called a new world into exist- 

 ence in the miil-Atlantic to explain the difficulties of paleozoological distribution in 

 the old world : but, on the other hand, a school composed mainly of zoologists have 

 adopted a more aquatic attitude by accepting the theory of the permanence of 

 oceans and continents, which leaves these difficulties unexplained. Certain 

 physical arguments have been adduced in support of gins view, but they do not 

 seem of any great value, and the whole question seems to turn on zoological, and 

 especially on paleontological distribution. If the Atlantic has hem permanently a 

 deep ocean hasin no such littoral tropical formscould have entered Europe from the 

 wesl except during periods when the arctic area enjoyed a temperate climate, ami 

 a theory which postulates a series of such warm periods would he unsatisfactory 

 even if there were not evidence in some cases against the " northwest passage." 



The question is one of- e importance to workers inmosl departments of paleon- 



tologj . The phylogenisl « ho accepts the theory of the permanence of oceans and 

 continents is likely to train the branches of his phylogenetic tree along very differ- 

 ent lines IV those that would he preferred by one who admitted the possibility 



