IV. — Comparisons of the Bermudian, West Indian, and Bra- 

 zilian Coral Faunae. By A. E. Verrill. 



Plates x-xxxv. 



1. — Characteristics of the Bermndian Coral Fauna.* 



The coral-fauna of the Bermudas must be regarded as a detached 

 colony of the more hardy species that have migrated from the West 

 Indies through the agency of the northward currents, by which their 

 free-swimming larva? have been carried to these islands. 



Therefore the particular species that have become established 

 there, have been determined both by the duration of their free larval 

 stages and by their ability to endure the cooler waters of this area. 



It has been a process of natural selection, in this sense, though it 

 probably has not yet gone far enough to differentiate a single new 

 species nor even any marked varietal forms. f 



Probably most of the species have migrated directly from the 

 Bahamas. How long a time is required for drifting objects to travel 

 from the Bahamas to the Bermudas is not known. The distance is 

 rather more than 700 miles, but any floating object would not travel 

 in a straight line, so that it would, most likely, travel nearly 1,000 

 miles in such a journey. At the rate of 1 mile per hour the north- 

 ward drift would be 1008 miles in 42 days, or 720 miles in 30 days. 

 Probably the average rate of the current, in this region, may not be 

 much greater than this. 



* After this article was in type I received the important report by Dr. T. W. 

 Vaughan on The Stony Corals of Porto Eican Waters (Bulletin U. S. Fish Comnt. 

 for 1900, ii, pp. 289-320, with 38 plates, Dec, 1901). Hence I am able to make 

 use of it only by inserting, in the synonymy, references to it, and especially to 

 the important plates, reproduced from photographs. 



But as Mr. Vaughan uses the same nomenclature and repeats the same argu- 

 ments to sustain his conclusions that he published in his preceding paper of 

 1901 (Fossil Corals of the Elevated Eeefs of Curacoa, etc.), a better opportunity 

 to refer to his work would have involved no changes in my own conclusions. 



f Two new species that I have now described from the Bermudas (Mussa annec- 

 tens and Mussa (Isophyllia) multiflora are not yet known from the West 

 Indies, but they will probably be found there when carefully looked for. 



