THE NAUTILUS. 



15 



knowing. This long period of separate evolution we further infer, 

 was followed by a brief period of union during which forests ex- 

 tended from the Waianae mountains across the valley to the western 

 part of the Main Range. This connection must have been quite 

 recent, within the life of existing species, for in several cases the 

 same species is found in both ranges. A few forms have been 

 specifically differentiated since the migration, or possibly they may 

 have died out in the original area. At the present time the forests 

 have receded up the mountains, and no migration from range to 

 range is possible. Moreover, there has doubtless been extinction of 

 many forms which once inhabited the lower region. 



Most of the migrating species are exceptionally virile forms, shown 

 by their rather wide distribution and tendency to form varieties in 

 their home ranges. Such are A. spirizona, A. rubens, A. reticulata, 1 



A, crassilabrum. 



In the following list of Oahuan Amastrse the Main Range species 

 are given in the left, Waianae species in the right column. A few 

 species of unknown habitat and some named varieties are omitted as 

 unessential. 2 The new names for the latest discoveries of Messrs. 

 Thaanum and Spalding and Dr. Cooke will be defined in the next 

 number of the Manual of Conchology. Names of fossil species are 

 prefixed thus t- 



Forms which are believed to have orio'mated in the Main Range 

 are printed in Roman type ; those of Waianae origin in Italics. 

 Main Range. Waianae Range. 



(Series of A. umbilicata^) 

 Sola. 



t Antiqua (Ewa) ? Heliciformis Thwing. 3 



1 Amastra reticulata was first named from the derivative migrant in the 

 Waianae Range, instead of from the descendants of the parent stock in the 

 Main Range, a circumstance which might lead to an erroneous idea regarding 

 the origin of the several forms. 



2 Ackatinella clongata Newc., an Oahuan species, has been omitted for want 

 of a knowledge of the apical sculpture to fix its systematic position. It may be 

 a sinistral member of the sjiirizona group, related to A. tenuispira, or it may 

 possibly prove to belong to the group of A. soror. 



3 Mr. Thwiug has figured as Amastra helidformis Ancey a shell resembling 

 Amastra agglutinans Newc., of Maui. It can hardly be Mr. Ancey's species, 

 which belongs to Pterodiscus (see Manual of Conchology, pi. 36, figs. 1, 2, 3), 

 and is much more depressed than Thwing's figure. See Occasional Papers 



B. P. B. Museum, III, no. 1, pi. 3, fig. 17. 



