vi Introdiinion . 



from the Ewa district. It is true that Dr. Newcotnb's plate of 

 A. cestzis looks much like some forms of A. hwgida, but with the 

 shells before one the many real differences would be clear. 



While different species may be found in the same locality, 

 and indeed on the same tree, as a rule, with some exceptions, the 

 same species is not found in widely separated localities. This 

 seems to be one of the distin(5live characteristics of this genus. 

 Each species has for its home or metropolis, a valley or a succes- 

 sion of valleys where it may be found in abundance. As we leave 

 this metropolis the examples found become fewer and fewer. 

 Many species are both sinistral and dextral, others rarely so, some 

 never both. Some species are very constant in color marking and 

 shape, others vary greatly. During a dry season, or on exposed 

 and dry ridges, mature shells will be smaller and less shining than 

 under other conditions. A shell should not be described as a new 

 species without a sufficient number of examples from a definite 

 locality, to show the various color varieties. 



In this paper there has been no definite attempt to reduce the 

 number of species, although this is a work that should certainly 

 be done. Some attempt, however, has been made to give a natural 

 grouping, and with the original descriptions and a good series of 

 the shells, each student and colledlor will be able to decide for 

 himself to a large extent what shells are true species, and what 

 names should be considered as synonyms, or simply color varieties. 

 The descriptions are arranged as far as possible in geographical 

 groups under each sedlion, the shells of Oahu first being con- 

 sidered. It is only by a careful study of the geographical locali- 

 ties of the shells that the species can be corredlly separated. Mr. 

 D. D. Baldwin has given much valuable information in his dis- 

 cussion of the "Geographical Distribution of the Achatinella," as 

 will be seen from the following extract from his excellent paper: — 



"The facts relating to the geographical distribution of the 

 Achatinella and the development of so large a number of species 

 within the limits of small areas, are very remarkable and interest- 

 ing, and have presented problems bearing on the theories of evolu- 

 tion. Each island has its own peculiar species, and not only 

 species, but its own peculiar types, or groups of species of similar 

 form. Again, on the islands where there has been a full develop- 

 ment of Achatinella, each principal mountain ridge and valley has 

 its own peculiar species which are found nowhere else ; the species 



