viii Introduction. 



valley and ridge has its own peculiar species or varieties ; but all 

 the arboreal species can be referred to seven leading types, these 

 differ much from the Oahu types, and do not present the same 

 varieties of form or color. The prevailing colors are white and 

 dark brown with all the intervening shades of either, plain or 

 variously arranged in bands or zigzaged lines. 



"East Maui. — The distribution of Achatiuella on this part 

 of Maui is not full}' known. All its mountain gorges and ridges 

 concentrate around the rim of the immense crater of Haleakala, a 

 circumscribing bound of nearly thirty miles in extent. The almost 

 impenetrable forest on the mountain slopes to the east and south 

 of the crater, comprising a belt of twenty miles long and six 

 miles wide, remains unexplored, and its molluscan life is unknown. 

 The woodlands on the northwest slope of the mountain facing 

 West Maui furnish 29 described species of Achatiuella ; but they 

 are the same or unmistakable counterparts of those found on West 

 Maui. The narrow depression of land between East and West 

 Maui has led many to infer. that they were originally separate 

 islands; this similarity of shell types would seem to indicate that, 

 if ever separate, they must have been united before the develop- 

 ment of molluscan life ; otherwise we should expect to find the 

 types of East and West Maui differing as much from each other as 

 do those of Maui and the contiguous islands of Molokai and Lanai. 



"Molokai. — The distribution of Achatiuella on this island 

 presents some new features not observed on any other island. 

 The island is forty miles long with a width of only seven miles ; it 

 is about one-third the size of Oahu, and, like it, has a mountain 

 range extending nearly thirty miles through its length. The range 

 is furrowed on each side by deep valleys. Some of these moun- 

 tain gorges are very wide and cut deep into the narrow axis of the 

 island. The larger ones have proved an effectual barrier to the 

 migration of the shells. The island is thus divided into three 

 natural sections, and each section retains its own peculiar species 

 without intermingling with those of the next section. Molokai 

 furnishes 25 described species which are about equally divided 

 between the three sections of the island. These shells exhibit 

 more variety of form and color than those of Maui, and have peculi- 

 arities which separate them entirely from types of other islands. 



"Lanai. — This is the smallest and most arid of the shell- 

 producing islands. Its area is 100 square miles, of which prob- 



