Introduilion . vii 



of each ridge or valley being often connedled with those of the 

 next by intermediate varieties. 



"Another important fact observed in the distribution of the 

 Achatinella is, that on a mountain chain with many culminating 

 peaks, the tendency is to a divergence of species ; while on an in- 

 dividual mass of mountains concentrating toward a single culmi- 

 nating peak, the tendency is to a convergence of species. 



"The struclure of the Hawaiian Islands is volcanic ; and in 

 studying the distribution of shells over them it is important to note 

 the relative ages of the several islands. Geologically speaking 

 Kauai is the oldest : next in the series is Oahu ; then Maui with the 

 adjoining islands of Molokai and Lanai ; and last comes Hawaii, 

 in the southern portion of which volcanic fires are still raging. 



"Oahu. — The development of Achatinella on this island, both 

 as regards number and variety of form and color, has been greater 

 than on any other island of the group. Unlike most of the other 

 islands, which have individual mountain masses, Oahu has tw'o 

 true ranges or chains of mountains, a longer and a shorter one, 

 with many independent culminating peaks. The aggregate length 

 of the two ranges is fifty miles. The sides of these ranges the 

 entire length are furrowed with deep valleys separating lofty 

 ridges. These valleys and ridges are the home of the Achatinella. 

 Each valley and ridge has its own distinct species which are con- 

 nected with those of the next valley and ridge by a multitude of 

 intermediate varieties presenting minute gradations of form and 

 color. These two ranges of mountains have already furnished 227 

 distinct described species of Achatinella. The number of varieties 

 has been estimated as high as 800 or 900. All these species and 

 varieties are found in an area of less than 120 square miles, and 

 a considerable portion of the longer range remains yet to be ex- 

 plored. These species have all the various shapes from globose 

 conical to ovate and elongate conical, and present almost every 

 ix)ssible shade and variety of coloring, pure white to jet black, and 

 all the shades of green, rose, yellow, brojvn and ash. Sometimes 

 several of these colors are combined in one species, either in regular 

 or irregular bands, or te.ssellated, marbled or zigzaged designs. 



"Wkst M.\ui. — On this part of Maui we have the converse of 

 Oahu. Its individual ma.ss of mountains, clustering around one 

 common centre peak. 2000 feet higher than any part of Oahu, fur- 

 nishes only 30 described species of Achatinella, each principal 



