Vol. 51.] AND PHYSICAL GEOLOGY OF THE WEST INDIES. 301 



This view has heen arrived at independently by students of the 

 mollusca, the echinoids, and the fishes. In each of these groups 

 we find a certain well-marked resemblance between the faunas of 

 the two sides of Central America. This may consist either in 

 the occurrence in both of identical species, or of closely allied or 

 equivalent species of the same genera. Thus P. P. Carpenter * has 

 given a list of 35 species of mollusca which live on both coasts of 

 Central America; of 34 species which may do so ; of 41 species which 

 are separated from those of the other side by trivial differences, and 

 of 26 species analogous to others on the western shores. "With a 

 caution, however, which those who have quoted these figures have 

 not always shared, Carpenter merely asked whether these facts 

 might not imply a connexion between the two oceans across Central 

 America in Glacial times. 



Prof. A. Agassiz 2 has been no less emphatic as to the resemblances 

 between the echinoid faunas of the two seas, and even more cau- 

 tious in his conclusions. In 1869 he published a list showing that 

 all but three of the genera of echinoidea that live on the west coast 

 have representative species in the east-coast fauna. This list has 

 been used by Sir Wy ville Thomson 3 as a typical case of the ' law 

 of representation,' with the natural inference that the two faunas 

 must have had a common ancestor at no distant period. Prof. A. 

 Agassiz has again called prominent attention to these facts in a 

 chapter and elaborate table in his Report on the 'Blake ' Echini. 4 

 But though these facts have been used to support the case of the 

 recent date of the Panama submergence, as we shall see later on, 

 Prof. Agassiz went rather to the other extreme and made it older 

 than is necessary. 



The third main group of animals that has been used to prove the 

 recent age of the connexion is that of the fishes. It was stated 

 that ' with scarcely any exceptions the genera are identical, and of 

 the species found on the Pacific side nearly half have proved to be 

 the same as those of the Atlantic' It was therefore contended 

 that the fishes proved ' the existence of communications between 

 the two oceans by channels and straits which must have been open 

 till within a recent period.' 5 



With such conclusions vouched for by such authorities, it is no 

 wonder that those who wished to deflect the Gulf Stream in order 

 to account for the cold of the Glacial climate felt fully at liberty to 



1 P. P. Carpenter, 'Report on the present State of our Knowledge with 

 regard to the Mollusca of the West Coast of North America,' Rep. Brit. Assoc. 

 for 1856 (1857), pp. 363-364. 



2 A. Agassiz, ' Preliminary Report on the Echini and Starfishes dredged in 

 deep water between Cuba and the Florida Reef, by L. F. de Pourtales,' Bull. 

 Mus. Comp. Zool. vol. i. (1869) pp. 301, 302. 



3 Wyville Thomson, ' The Depths of the Sea,' London 1873, pp. 13, 14. 



4 A. Agassiz, ' Report on the Results of Dredging .... by the .... Blake,' 

 vol. xxiv. pt. i. ; ' Report on the Echini,' Mem. Mus. Comp. Zool. vol. x. (1883) 

 no. 1, ' Origin of the West Indian (Caribbean) Echinid Fauna,' pp. 79-94. 



6 A. Gunther, ' Introduction to the Study of Fishes,' 1880, p. 280, and 'The 

 Fishes of Central America,' Trans. Zool. Soc. vol. vi. (1868) pp. 397-402. 



