378 HYATT: GENEALOGY OF ACHATINELLID^E. 



proper is a highly colored group of arboreal shells, in which 

 we may include Perdicella which is also very nearly connected 

 with Amastra, through species like Laminella gravida of 

 Oahu that have spires of dark brown similar to those of 

 some shells of Amastra rubens, cylindrica, etc., that have a 

 coarse, friable periostracum and elongated spires showing a 

 decided tendency to evolve turritelloidal forms. The basal 

 volutions are more globose and the apex more acute in 

 gravida, but this species is an intermediate form in other 

 respects leading not from the semi-arboreal turritelloidal 

 Amastras into Laminella, but from the turritelloidal ground 

 shells into this genus or group, which includes the very dis- 

 tinct and highly colored Lam. sanguinea and other forms 

 with turritelloidal spires that are found mostly in semi- 

 arboreal habitats on low bushes, ferns, etc., according to 

 Cooke and Gulick. 



The apex in the nepionic stage is smooth in Laminella and 

 of the same dark horny aspect as it is in most of the species 

 of Amastra on Oahu, and the columella is highly developed, 

 twisted and perforated, as it is in Am. turrit ella and its 

 allies. 



In the genus Amastra the shell is usually dark brown. 

 The species live on the ground and are present in all the 

 islands of the Hawaiian group that are inhabited by land 

 shells. The species, as in all other genera, are so closely 

 connected that it is very difficult to separate them. They 

 have a single spiral fold on the lower edge of the columella. 

 This fold is not characteristic of the genus but is shared 

 in common with all the other genera of the family Achati- 

 nellidce, occurring only in these islands. Nevertheless there 

 are two marked deviations from this homogenetic character- 

 istic, for in many individuals among a limited number of 

 species, all of the genus Amastra, there is a slight tendency 

 to form a second fold above this, but it does not take the 

 definite form of a tooth-fold except in some very rare ex- 

 amples, and it is in these an obviously sporadic development 

 having no genetic significance. 



In about fifty thousand shells of this family this occurs 



