234 AMASTRA, LANAI. 



D. Thaanum. Length 10.3, diam. 6.5, aperture 5.3 mm. ; 

 whorls. 



Subgenus AMASTRA s. sir. 



Imperforate or narrowly rimate Amastrae with the embry- 

 onic whorls typically flattened, costate, and carinate above the 

 suture (the carina sometimes concealed), rarely they are con- 

 vex and striate. Cuticle generally marked with zigzag or an- 

 gular stripes or spots. Type A. magna. 



Distribution : Molokai, Maui and Lanai. 



The variation in embryonic sculpture which is occasionally 

 encountered in this subgenus is extraordinary, though in the 

 great majority of specimens and species only the costate and 

 carinate type of embryonic shell is found. The main excep- 

 tions are in the series of A. magna, where the costation is weak 

 in A. violacea and wanting in A. nubilosa; and the series of 

 A. nigra, where that species has two embryonic forms, figured 

 in pi. 43, figs. 1 and 3, and A. subcrassila'bris has an embryo 

 of the type shown in pi. 43, fig. 3. There are also a few other 

 less aberrant cases of non-typical embryos in other series of 

 the subgenus. This seems to be a case where the embryonic 

 stage mutates independent of the later stages, a condition 

 encountered in the Muricidcc, Buccinida, etc., and sometimes 

 recognized under the term ' ' heterostyly. ' ' 



Series of A. pusilla. 



Small Amastra? with the embryonic whorls costate and cari- 

 nate, later whorls banded beneath a thin, yellowish, unfigured 

 cuticle. 



The single species placed here resembles A. petricola and 

 A. abavus of Molokai in form and coloring, but differs en- 

 tirely in embryonic sculpture. It is probably related to A. 

 tricincta and its allies of Molokai. 



56. A. PUSILLA (Newcomb). PI. 17, figs. 8, 13, 15. 



Shell dextral, conically ovate; apex acute; whorls 6, plano- 

 convex; suture above but lightly impressed, below strongly 

 marked; lip simple; columella short, with a twisted plait; 

 epidermis light-brown, often encircled by narrow white bands. 



