218 AMASTRA. OAHU. 



below the suture by a broad pale dirty flesh-colored zone. 

 Whorls 6!/2, the first 3y 2 nearly flat, blackish, the rest convex; 

 suture hardly margined. Aperture white; peristome with a 

 thin blackish-purple edge, lightly bordered within; columella 

 roseate, provided with a laminiform basal fold (and sometimes 

 one or two tubercles). Length 20, diam. 12 mm." 



Oahu, western part of the northeastern range: Wahiawa, 

 type loc. ; also found in all the valleys from Kalaikoa to Wai- 

 mea, sometimes on the ground but more frequently on trees 

 (Gulick). Type in British Museum. 



Amastra nigrolabris Sm., GULICK and SMITH, P. Z. S., 1873, 

 p. 85, pi. 10, f. 9. PPR., Monogr., viii, p. 238. Ackatinella 

 mgrolabris THWING, Orig. Descriptions, p. 148, pi. 3, f. 15 

 (uncharacteristic). Laminella nigrolabris Smith, W. G. BIN- 

 NEY, Ann. N. Y. Acad. Sci., iii, 1884, p. 98 "lingual dentition 

 as in mastersi. ' ' 



Typically the last whorl of this snail is light-colored from 

 suture to, or nearly to, the periphery, 2 or 3 preceding whorls 

 being light with a dark band above the suture, and the out- 

 lines of the spire are a little concave (figs. 14, 15, Wahiawa.) ; 

 but in most of the lots before us there are also specimens in 

 which the light color is confined to a narrow band below the 

 suture, generally shading into the dark 'basal color, but some- 

 times as sharply defined as in spirizona. Such shells are re- 

 ferable to Swainson's acuta. They are figured in pi. 35, fig. 

 10, and pi. 40, fig. 16 (Kawailoa), and pi. 35, fig. 12 (Wai- 

 mea) . There are also transitional specimens, as Mr. Sykes has 

 pointed out, both in color and shape, between spirizona and 

 mgrolabris. 



The fact seems to be that a formerly widespread stock has 

 been diversely modified on the two ranges. On the northern 

 range the herd is composite, consisting of a mixture of spiri- 

 zona forms (which might be called acuta Swains, if they need 

 a name), with a broad-banded mutation peculiar to that range 

 (typical mgrolabris}, the latter predominating. This color- 

 change is apparently coincident with a change in progress 

 from terrestrial to arboreal habits, nigroldbris living on 

 . spirizona generally on the ground. 



