THE VIRGIN ISLANDS. .229 



recorded species, of which two are of accidental occurrence, while fourteen are 

 exclusively found upon Porto Rico; though a number of others, as Stejneger 

 has shown, have but a circimiscribed range, occurring on Porto Rico, and either 

 Vieques, Culebra, or Mona Islands. Unlike either Haiti, Cuba, or Jamaica, 

 Porto Rico has no genus of either reptiles or amphibians that is peculiar to it. 

 This fact would seem to lend weight to the theory which has already gained 

 some supporters, that the actual land area of an island has a certain more or less 

 definite relationshi]i to the species population of that island; and the larger the 

 island is, the greater the nmnber of genera and species that will be found on it. 

 Cuba, the largest of the Antilles, and Haiti, the next largest, are in this way 

 sharply set off from both Porto Rico and Jamaica, which are far smaller than 

 either of the other islands, and more or less similar in size to each other. It is 

 interesting to note that the same condition of affairs obtains in the East Indies, 

 where Borneo, the largest island, has a greater number of species than Sumatra, 

 which is geograplaically much more closely related to the mainland, and which 

 might be supposed to have received probably a larger number of mainland types 

 than any of the other islands. 



The Virgin Islands. 



Owing to the great depth of water found between this group and the rest 

 of the Lesser Antilles, it might be supposed that a faunal boundary would be 

 found to exist here comparable to that which was formerlj^ supposed to exist in 

 the East Indies between the islands of Bali and Lombok. This, however, is not 

 exactly the case. Of the Central American genera which do not reach the Lesser 

 Antilles, Hyla does not get to Porto Rico; Bufo reaches Porto Rico, but no 

 further; Liocephalus extends to Haiti only; Celestus to Porto Rico. Amphis- 

 baena, however, is found upon St. John, St. Thomas, and St. Croix; so that, while 

 none of these genera extend so far as the Lesser Antilles, these islands form the 

 limit of occurrence for only one of them; whereas the many characteristic 

 Antillean genera of both reptiles and amphibians such as Eleutherodactylus, 

 Sphaerodactylus, Anolis, Ameiva, Mabuya, Typhlops, Alsophis, and Leimado- 

 phis occur throughout the entire chain, without any reference whatever to a 

 faunal boundary Une between these islands. The group consists entirely of 

 land masses of insignificant area, and with a correspondingly small number of 

 species upon each island. 



