284 AMASTRA, MAUL 



or thread-striate embryonic whorls, later whorls with a thin, 

 dark cuticle, sometimes longitudinally streaked but never 

 mottled or figured; columellar lamella receding and steeply 

 ascending, generally small ; axis rimate or imperf orate. Type 

 A. hutchinsonii. 



Distribution, Lanai, Molokai, Maui and Hawaii. 



These forms have been classified with Laminella by many 

 writers, as Baldwin and Sykes, while others have considered 

 them sinistral Amastra, directly related to dextral forms of 

 the region, a view taken by Borcherding, Hyatt, and appar- 

 ently by Thwing. Differences in the embryonic whorls and 

 the color pattern indicate that the relationship between these 

 shells and the dextral Amastraa of Maui and Molokai is not 

 close, though both groups are of common ancestry. The sin- 

 istral species form a natural group, which seems to have split 

 off from Amastra at an early period. 



The embryonic sculpture and dark, inornate coloration 

 separate Eeteramastra from Laminella. 



Professor Hyatt intercalated these forms among dextral 

 shells in various groups, as may be seen by reference to his 

 classification, Appendix II. 



Key to species of Heteramastra. 



a. Diameter of shell equal to or exceeding half the length; 

 surface not strongly rugose, smoothish or with weak 

 sculpture. 

 6. Spire not contracted near the summit. 



c. 12x6.9 mm. ; Maui. A. s. laticeps, no. 86b. 



c 1 . 10x5.5 mm.; last whorl swollen; blackish; Lanai. 



A. fraterna, no. 55. 

 6 1 . Spire noticeably contracted near the summit. 



c. Moderately solid; spire brown, last whorl lighter 



colored; Maui. A. soror, no. 86. 



c 1 . Thin, shell of nearly uniform dark color; about 



5% whorls. 

 d. Brown, thin, 10x5 mm.; Maui. 



A. subsoror, no. 87. 

 d 1 . Blackish, obese, 10.3x6.5 mm. ; Lanai. 



A. fraterna, no. 55. 



