156 AMASTRA, OAHU. 



AMASTR^E OF OAHU. 



Oahu has representatives of four subgenera or sections of 

 Amastra. Amastrella and Cyclamastra are widely-spread 

 groups in other islands, while Metamastra and Paramastra 

 are special to this one. A single species, A. elongata Newc., 

 has been referred to Heteramastra, but its claim to a place in 

 the Oahuan list is questionable. 



The island consists of two volcanic masses, a higher, prob- 

 ably older western mass, the Waianae or Kaala range, and a 

 larger, lower, eastern or Koolau range, which has been shown 

 by Dana to be later, or at least to have continued in active 

 eruption later than the other, by the encroachment of its lava 

 streams over the base of the Waianae range. The saddle be- 

 tween these ranges reaches an elevation of nearly 900 feet. 

 It is arid or grassy, and supports no Achatinellida : 



Pterodiscus, Cyclamastra and Laminella are common to 

 both ranges. Metamastra and Amastrella are characteristic 

 of the Koolau range, the former with 15, the latter 9 species. 

 Three forms of Metamastra, all varieties of Koolau species, 

 occur in the Waianae range, and there are two Waianaean 

 Amastrella, one varietally connected with a Koolau species, 

 the other specifically distinct. 



Armsia and Planamastra, each with one species, are known 

 from the Waianae range only. Paramastra, with 7 species, is 

 also characteristic of the Waianae range. Two of these species 

 occur also in the Koolau range, where there are also two dis- 

 tinct species of the same group. The cornea group is like- 

 wise probably of Waianaean origin, two species being from 

 that range, and two, rare and local, in the Koolau range. 

 Not much weight is to be attached to this series, since the re- 

 lationship of the Waianae and Main Range species is rather 

 uncertain. See pp. 138-9, where the species of both ranges 

 are enumerated. 



It appears from the data in hand that both eastern and 

 western areas existed as independent evolution-centers for a 

 period sufficiently long for the evolution of distinct sub- 

 generic groups of Amastras in each, while Planamastra and 

 Armsia became differentiated in the Waianae, and various 



