AMASTRA. 135 



the name Laminella would take precedence over Amastra for 

 the group so formed. 



Characteristics of Amastra. 



THE COLUMELLAR LAMELLA is present from the later em- 

 bryonic stages. How early it appears we do not know, but 

 in half-grown embryos examined it is either distinct or rep- 

 resented by a spiral cord. It is absorbed as growth pro- 

 ceeds, leaving the remaining portion about a half-whorl long. 

 Very rarely, in old shells, the lamella is wanting, without 

 other evidence of abnormality in the shell. Two instances 

 have been noted, A. violacea wailauensis, pi. 39, fig. 13, and 

 A. lava, pi. 48, fig. 15. The lamella is subhorizontal or bent 

 downwards in most Metamastrge. It is small and oblique in 

 Amastrella, Cyclamastra and Carelia. 



In some forms of Amastra the columellar lamella is 

 doubled, or rather, there is a second fold developed above 

 the usual lamella. This structure is usual in the biplicata 

 series of Lanai, and it occurs as an occasional mutation in 

 the Spirizona series of Oaliu. A similar duplication of the 

 columellar lamella exists in Leptachatina leucochila Gulick 

 (p. 73). In a few species of various groups there is a low 

 callous lump on the parietal wall a short distance within, 

 not sufficiently definite to be called a tooth, and so far as we 

 know rather rarely developed in any species. It has been 

 noted in A. decorticata (pi. 33, fig. 7), A. antiqua, A. vio- 

 lacea and A. knudseni. 



THE CUTICLE, in primitive species, such as the Kauaian 

 and Hawaiian Amastrellas, is thin and pale yellowish. In 

 many species of Oahu, Molokai, Lanai and Maui the outer 

 layer is dark, usually dull, and more or less completely de- 

 ciduous, always transient in front of the aperture, exposing 

 the thin, closely adherent and glossy inner layer, which is 

 generally of a different color and lighter shade. The outer 

 cuticle is frequently mottled or marked with zigzag streaks 

 in species of Lanai, Molokai and Maui, somewhat as in Lami- 

 nella ; but in other islands it is plain or varied with streaks 

 along growth-lines. The inner cuticle is transparent, show- 



