AMASTRA, OAHU. 209 



biplicata group. This fold is probably hoinoplastic, not homo- 

 logic, in the 'two groups ; for the biplicatce 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. 



b. Apex rather large, 'bulbous; chestnut to buff, suture 

 paler. A. turritella, no. 47. 



ft 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. 

 b. Spire concavely turrite, diam. half the length. 



A. t. aeia, no. 47a. 

 ft 1 . Spire straightly oonic, stouter. 



A. t. waiawa, no. 47&. 

 b. Diam. decidedly more than half the length. 



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

 11.5 mm. A. spirizona, no. 48. 



