HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 267 



ing forms. The recent faunas of the opposite side of the Isthmus are 

 so distinct from each other that the only logical deduction that can be 

 made from the few identical species is that they are the survival of a 

 communion of waters which took place in very remote time. 



On the contrary, if there had been communion at so late an epoch 

 in Pleistocene time, the present species of the opposing sides of the 

 Isthmus would so resemble each other that they would hardly be dis- 

 tinguishable. The testimony against this Pleistocene connection is 

 strongly presented by all sides of biologic research. 



The species and genera of corals of the two faunas of the Atlantic and 

 Pacific coast, according to A. E. Verrill, 1 are entirely distinct, a conclu- 

 sion with which Mr. Gregory fully concurs, who expresses himself against 

 a submergence of the Isthmus since Pliocene times. 2 



Belt 3 states " that the mollusca on the two coasts, separated by 

 the narrow Isthmus of Darien, are almost entirely distinct. ... In the 

 Caribbean province, which includes the Gulf of Mexico, the West Indian 

 Islands, and the eastern coast of South America, as far as Rio de Janeiro, 

 the number of marine shells is estimated by Prof. C. E. Adams at not 

 less than 1,500 species. From the Panamic province, which, on the 

 western coast of America, extends from the Gulf of California to Payta 

 in Peru, there have been catalogued 1,341 distinct species of marine mol- 

 lusca. Out of this immense number of species, less than fifty occur on 

 both sides of the narrow Isthmus of Darien. So remarkably distinct 

 are the two marine faunas, that most zoologists consider that there has 

 been no communication in the Tropics between the two seas since the 

 close of the Miocene period, whilst the connection that is supposed to 

 have existed at that remote epoch, and to account for the distribution 

 of corals, whilst advocated by Professor Duncan and other eminent men, 

 is disputed by others equally eminent. No zoologist of note believes 

 that there has been a submergence of the laud lying between the 

 Pacific and the Atlantic since the Pliocene period. See also Greg- 

 ory 4 for the mollusks, and Fisher, 5 Jordan, 6 and Evermann and 



1 Proc. of the Essex Institute, 1866, p. 323. 



2 " On the Comparison of the Coral Fauns of the Atlantic and Pacific Coasts of 

 the Isthmus of Darien, as bearing on the supposed Former Connection between the 

 two Oceans." American Naturalist, Vol. III. p. 500 (1869). 



3 " Naturalist in Nicaragua," page 264. 



* Quart. Journ. Geol. Soc, Vol. LI. No. 203, pp. 302, 303, London, August, 1895. 



5 P. Fisher, " Manuel de Conchologie," 1887, p. 168. 



6 David S. Jordan, " A List of Fishes known from the Pacific Coast of Tropical 

 America, from the Tropic of Cancer to Panama," Proc. U. S. Nat. Mus., Vol. VIII. 

 pp. 361-394, especially pp. 393, 394 (1885). 



