138 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Pedro Gonzales and San Jose Islands were not visited ; lying a little 

 apart from the other islands, these two might prove to be intex'esting, 

 but time did not permit of tlieir being explored. 



The vertebrates of the Pearl Islands are derived for the most part 

 from the adjacent mainland, being eitlier the same as, or slightly 

 differentiated, island races of widely distributed Panamic forms. There 

 are, however, some striking exceptions to this rule. Among the mam- 

 mals, for instance, the nearest ally of the island vesper rat — Zygodon- 

 tumys seorsus — seems to be Z. hrevicauda of Trinidad ; and a species 

 of Loncheres allied to the Colombian L. caniceps occurs in the Pearl 

 Islands, though the genus is as yet unknown from anywhere else north 

 of South America proper. 



Among the birds the more peculiar cases of distribution are the yellow 

 honey-creeper, which is not nearly related to Coereha mexicana of the 

 adjacent mainland, but finds its closest ally in G. luteola of the Carib- 

 bean coasts of Colombia and Venezuela ; the Phaethornis of the islands, 

 which is related to P. anthophilus of central and eastern Colombia and 

 Venezuela ; and the ant wren, which, though very distinct, is a repre- 

 sentative of Formicicora intermedia of Venezuela and Colombia. 



Geologists appear to know very little about the Pearl Islands, and I 

 can find nothing in print. Mr. Brown collected specimens of rock, and 

 these, according to Professor Crosby, are of volcanic origin. From what 

 little I can gather, I infer that the Archipelago de las Perlas has never 

 been connected with the mainland since the elevation of the isthmus 

 and the separation of the waters of the Bay of Panama from the 

 Caribbean Sea. 



The islands lie in the middle of the Bay of Panama, distant about 

 twenty miles from the nearest point on the mainland. The larger ones 

 are hilly and covered with a dense, luxuriant tropical forest, with the 

 shores in many places fringed by mangroves. The waters of the Bay of 

 Panama all about the islands are very deep. 



The collections of reptiles, amphibians, and fishes will be reported 

 upon in the third paper of this series. 



Mr. Brown also made a small collection of trees and woody shrubs. 

 These an-ived in splendid condition and have been presented by Mr. 

 Thayer to Prof. C. S. Sargent. 



