Vol. 51.] AND PHYSICAL GEOLOGY OP THE WEST IKDIES. 303; 



the work of the latter authors, 1 who described the ' fish faunse of 

 the two coasts as being essentially distinct ' ; they conclude that 

 ' there has not been, at any comparatively recent time, any water- 

 way through the Isthmus of Panama.' They accept the fish fauna 

 as composed of 1307 species, and, excluding 16 species of such wide 

 distribution that their evidence does not count, they estimate that 

 only 4-3 per cent, are common to the two shores. They add, more- 

 over, that they think that the mollusca yield 'even stronger evidence 

 of the remoteness of the time when the means of communication 

 between the two oceans could have existed.' 



With the corals the evidence is still more conclusive. Two more 

 different coral faunas than those of the West Indies and Panama 

 could hardly be found. There is not one species common to the 

 two. Not only so, but the genera are nearly all different. Ortmann '-' 

 has recently published a list of genera from the two coasts to 

 emphasize this fact. Verrill has repeatedly called attention to the 

 almost complete difference between the two faunas, not only with 

 species and genera, but also with families. He has summarized the 

 results as follows: — 'No species are found to be identical, while even 

 the genera and families show remarkable contrasts. Thus the numer- 

 ous genera and families of reef-building corals, so abundant on the 

 Atlantic side, are wholly wanting on the Pacific, with the exception 

 of Porites, which is represented by three or four small species. 

 Massive Astraeans, Mceandrina, Diploria, Manicina, Colpophyllia, 

 Agaricia, Sideratfrcea [Astrcea], Oculina, Madrepora, Millepora, 

 are wholy unknown in the Panama fauna. But Pocillopora, 

 Montipora, and Pavonia, genera unknown on the Atlantic side, 

 are represented, the last by two gigantic species. Among the 

 Halcyonoid Polyps we find an equal contrast, for Eunicea, Plexaura,. 

 Plexaurella, Pterogorgia, and many other very common Atlantic 

 genera are unknown on the Pacific side, where they are replaced by 

 numerous species of Psammogorgia, Litigorgia, and Eugorgia, which 

 are eminently characteristic of that coast.' 3 Elsewhere he concludes 

 ' that there has been no connexion [between the oceans], or at least; 

 none sufficient to materially change the course of the Gulf Stream, 

 since the commencement of the Tertiary period.' 4 



We may, therefore, conclude from the evidence of the recent 



1 B. W. Evermann and O. P. Jenkins, ' Report upon a Collection of Fishes 

 made at Guaymas, Sonora, Mexico, with Descriptions of New Species,' Proc.U.S. 

 Nat. Mus. vol. xiv. (1891) no. 846, p. 126. 



2 A. Ortmann, ' Beobachtungen an Steinkorallen von der Sudkiiste Ceylons,' 

 Zool. Jahrb. Bd. iv. Abt. f. Syst. (1889) p. 528. 



3 A. E. Verrill, 'On the Comparison of the Coral Faunse of the Atlantic and 

 Pacific coasts of the Isthmus of Darien, as bearing on the supposed Former 

 Connexion between the two Oceans,' Amer. Nat. vol. iii. (1869) p. 500. 



4 A. E. Verrill, ' On the Polyps and Corals of Panama, with Descriptions of 

 New Species,' Proc. Boston Soc. Nat. Hist. vol. x. (1866) p. 325. See also his 

 'Comparison of the Tropical Faunse of the East and West Coasts of America,' 

 in ' Notes on Radiata, No. 3,' Trans. Connect. Acad. vol. i. pt. ii. (1867) 

 pp. 339, 340. 



Q.J.G.K No. 203. z 



