AMASTRA, OAHU. 209 



biplicata group. This fold is probably houioplastic, not hoino- 

 logie, in the 'two groups ; for the bipUcatce show characters of 

 the cuticle of the typical group of Amastra, with which they 

 are closely connected by a chain of annectant forms. 



One of us (Hyatt) considered A. turritella "the probable 

 ancestor of the entire group" Paramastra. The other author 

 (Pilsbry) views the same species as one of the latest deriva- 

 tives a terminal twig of the spirizona-nigrolabris branch. 



Key to Species of Paramastra. 



a. Slender forms, the diameter usually less than half the 

 length. 



6. Apex rather large, -bulbous; chestnut to buff, suture 

 paler. A. turritella, no. 47. 



& 1 . Apex small, pointed. 



c. Small, slender shells, with little dull cuticle or 

 none. 



d. Glossy, thin ; white, yellowish or brown, 

 often variegated with spiral lines; 17x 

 7.5 mm. 



A. micans, no. 45 ; A. frosti, no. 45a, 

 d 1 . Very slender, thick, whitish with brown 

 apex and pinkish base; 17x6.5 mm. 



A. tenuispira, no. 46. 



c 1 . Stouter shells, with a. thin dull outer cuticle. 

 d. Spire convexly conic; 18.5x9 mm. 



A. cylindrica, no. 52. 



d 1 . Spire straight; length 17, diam. 8 to 8.8 

 mm. A. variegata, no. 53. 



a 1 . Stout, pyramidal shells, the diam. half the length or more. 

 &. Spire concavely turrit e, diam. half the length. 



A. t. aeia, no. 47a. 

 & 1 . Spire straightly conic, stouter. 



A. t. ivaiawa, no. 476. 

 &. Diam. decidedly more than half the length. 



c. Dark brown with a yellow sutural band; 21x 

 11.5 mm. A. spirizona, no. 48. 



