88 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



composition of the fauna is different, however, a phenomenon to be 

 examined in more detail later (Chapter XXVI). 



The Hawaiian Islands are the most completely isolated archi- 

 pelago, more than 3000 km. distant from the American coast, and as 

 far from Samoa. They form a group of volcanic islands extending 

 from northwest to southeast for about 475 km., and the individual 

 islands are well separated. Endemic forms consist of large series of 

 species of certain genera and smaller series of related genera which 

 combine into families. All the species and three-fourths of the genera 

 of land snails are endemic. The family Achatinellidae is especially 

 notable, with only a general relationship to the widespread Polynesian 

 genus Partula, and with highly primitive characters in its sexual 

 apparatus and mantle. 57 This family, with 14 genera and more than 

 300 species, is confined to the Hawaiian archipelago. Some genera are 

 confined to special islands, Carelia and Catinella on Kauai ; Bulimella, 

 Apex, and others on Oahu; Perdicella on Maui; Eburnella on Lanai. 

 Each of the valleys radiating from the mountains is often character- 

 ized by a special series of species. 58 Of 3325 species of insects, more 

 than 2700 are confined to the islands; 170 out of 200 species of sting- 

 ing Hymenoptera are endemic. The one genus Odynerus contains 86 

 species, which form two well-defined groups. 59 The aquatic birds be- 

 long for the most part to widespread species, and only 5 out of 24 

 species are endemic, while certain finch-like forms are wholly confined 

 to the islands, and 9 genera with about 40 species form a special 

 family, the Drepanididae. Each island on which a bit of the original 

 forest is left has its special species of each of the 9 genera, and 

 Hemignathus has 2 species, one large and one small, on each of the 

 islands Hawaii, Oahu, and Kauai. 



The Galapagos Islands present similar faunal characteristics. This 

 archipelago is situated on the equator about 900 km. west of Ecuador; 

 two ocean currents flow past them, one from the coast of Peru and 

 one from the gulf of Panama, but they are in a region of relatively 

 little wind. The land snails, whose dispersal may have been favored 

 by oceanic currents, are little specialized; most of the 46 species are 

 endemic, 60 but the genera are without exception found also in Central 

 or South America. Of the 46 genera of birds, 30 are cosmopolitan or 

 world-wide in the tropics, 8 are American, one antarctic, one Pacific, 

 and 6 endemic; the last are all fringillids. The 66 species of land 

 birds, with the exception of the widely distributed bobolink and the 

 cosmopolitan short-eared owl, are all endemic. The endemic genera 

 are richest in species: Geospiza has 23, Nesomimus, Certhidea each 8, 

 and C hamorhynchus 13; they make up a large majority of the land 



