304 Synopsis of the Genus Achatinella. . 



his typical specimens, enable me to express my opinions with 

 some degree of conficlence. 



I apprehend, however, that my labors are not entirely with- 

 out errors, which to some may appear inexcusable. We are 

 aware that " gentlemen will differ" as to what constitutes a 

 species, some judging that a slight variation in color or form 

 will warrant a separation, which by others will be classed as 

 only a variety. 



There is one position that will not admit of a question, and 

 that is, that all the young from a common parent, however 

 variable, must be considered as one species. To a limited 

 extent my opportunities for applying this test in practice have 

 been improved, and the results have influenced my opinions as 

 expressed in the following paper. 



It may be well to refer to several sources of error, which 

 should be carefully guarded against in an examination of the 

 shells of this genus. 



The arid districts upon the Sandwich Islands are often in 

 close proximity to those abundantly supplied with rain, — the 

 latter furnish the most favorable condition for the full growth 

 and development of molluscous animals. 



The heavy rains that occur during the winter months fre- 

 quently detach gravid mollusks from their natural positions, 

 and wash them to a drier level below. The young there 

 deposited diminish in size from the parent stock, and barely 

 obtain a stinted existence. These may readily be taken for 

 distinct species. The group that Dr. Gould has distinguished 

 as Lejrtachatina are peculiarly liable to these changes. 



Several of the beautiful species with a fine green epidermis 

 are changed by the collector to a yellow hue, by treating them 

 to hot water ; and even when cured in cold water, and suf- 

 fered to remain immersed for some days, the change is equally 

 effectual in disguising their true character. 



Ambitious collectors have not in all cases resisted the temp- 

 tation to remove portions of epidermis from shells varying some- 



