124 FAUNA HAWAIIENSIS 



generic characters, signifying with considerable precision (for I find the same result in 

 such other faunas as are available for calculation) that on an average it takes four and a 

 half times as long to produce a genus as to produce a species. 



In the Hawaiian fauna, however, the proportion of species to genera is unusually- 

 high, being 6 to i, and it may be asked why this is so. It appears probable that, 

 owing to the extremely limited character of the fauna, and the relatively very small 

 number of genera available in the first instance as a base of development, the generic 

 competition has not been sufficiently severe to promote a high rate of modification : 

 whilst the variety of situations presented under similar but slightly different conditions 

 (such as those depending on altitude, rainfall, and insular separation), is highly favour- 

 able for specific development. I shall show presently that even the existing endemic 

 genera are not all on the same footing. 



Comparison of Families with other Regions. 



Only 12 families are represented in this portion of the fauna, and two of these, 

 the Galleriadae and Pyralididae, only by species of undoubtedly artificial introduction ; 

 thus only lo are truly native, all of them being of world-wide distribution. In the 

 corresponding portion of the British fauna there are no less than 34 families ; yet all 

 those families which are represented in Britain by more than 1 2 species are present in 

 the Hawaiian Islands except the Arctiadae, Sterrhidae, and Notodontidae, and none 

 which are represented by less ; so that, except for those three families, the results are 

 in accordance with the law of chance. The New Zealand fauna so much resembles 

 the Hawaiian in its broad outlines that it may be worth while to compare them in 

 tabular form. 



