108 PROCEEDINGS OF WASHINGTON MEETING. 



(excluding tl 10 few patches of Pliocene sand in northern France) is that of Bel- 

 gium. This, however, contains but two British species, though as a rule the species 

 are allied; the main difference consists in the presence of some Mediterranean 

 species and the absence of the four genera of the western group. The richest of 

 the Belgian beds is the Diestian, which is older than our Coralline Crag. This, 

 therefore, suggests that the "western group," as we may call the second element 

 in the Crag fauna, did not reach Europe until post-Diestian times, and thus did 

 not penetrate so far east as Belgium. 



In this case the same suggestions as to the possible northern migration or the 

 floating across of the larvae might be made, and there is Less evidence on the sub- 

 ject than in the Miocene. The only well-known species of Temnechinus from the 

 Crag (7". woodi, Ag.) was probably viviparous, and it may be that the West Indian 

 species is so also; otherwise there is no evidence to directly disprove this second 

 hypothesis. As there is no known European Pliocene fauna north of the Crag, 

 and as the Pliocene series from the American mainland is also very scanty, there 

 is no such means of disproving the northern extension of these tropical or sub- 

 tropical forms ; hut had this happened we might have expected a much greater 

 mingling of the faunas of different zones of latitude than has happened. The 

 echinoidea of the European shore agree more closely with those of the correspond- 

 ing isotherms on the American side than with the faunas north and south of 

 them. The presence of Temnechinus maculatus at the Azores as well as in the 

 West Indies also further suggests that the connection was established somewhere 

 in the mid-Atlantic. 



Summary of Conclusions. 



A brief comparison of the successive echinoid faunas of Europe ami America 

 has thus been attempted, and it may he advisable briefly to summarize the con- 

 clusions arrived at. 



In the Carboniferous period there was an almost complete difference between 

 the two faunas, whereas in the succeeding Urgonien and Aptien the two faunas 

 are almost identical. But the Cretaceous period was marked by a gradual differ- 

 entiation; species ceased to lie common to the two areas, and the representative 

 forms became more distinct. In the Eocene and Oligocene the same independent 

 evolution seems to have gone on; the American fauna was rich in species of Cas- 

 s'ltlulux and Pygorhynchus, genera also common in the Cretaceous beds of the same 

 continent, and the faunas were more distinct than were the Cretaceous. During the 

 Miocene there was again a change: afresh connection was established that enabled 

 the echinoidea of corresponding latitudes in the new and the old worlds to com- 

 mingle ; and later still, in the Pliocene, there is evidence to show the introduction 

 into the European area of some American echinoids. The possibilities of this con- 

 nection across the Atlantic by free-swimming larvae or by the adults having worked 

 around the northern margin have been examined and evidence adduced against 

 them, and one case i> quoted in which the dissimilarities of fauna cannot be ex- 

 plained as due to difference of age. 



It is therefore urged that the comparison of the succession of the echinoid faunas 

 of Europe and America present a series of phenomena wholly incompatible with 

 the theory of tin' permanence of the great ocean basins. 



Remarks were made upon the topic of the paper by Mr. L. C. Johnson. 



