HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 267 
ing forms. Тһе 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. Тһе testimony against this Pleistocene connection is 
strongly presented by all sides of biologio research. 
The species and genera of corals of the two faunas of the Atlantio and 
Pacific coast, according to A. E. Verrill,! are entirely distinct, а conelu- 
sion with which Mr. Gregory fully concurs, who expresses himself against 
a submergence of the Isthmus since Pliocene times. ® 
Belt? 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 zoólogists eonsider 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 zoólogist of note believes 
that there has been a submergence of the land lying between the 
Pacific and the Atlantic since the Pliocene period. See also Greg- 
ory’ for the mollusks, and Fisher," Jordan," and Evermann and 
1 Proc. of the Essex Institute, 1866, p. 323. 
2 “On the Comparison of the Coral Faune 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). 
8 “Naturalist in Nicaragua,” page 264. 
4 Quart. Journ. Geol. Soc., Vol. LI. No. 208, pp. 302, 303, London, August, 1896. 
5 P. Fisher, “Manuel de Conchologie,” 1887, p. 108. 
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. 398, 894 (1885). 
