352 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



The shell is depressed-helicoid, almost lenticular. The early whorls 

 are flesh-colored, while the succeeding; turns have the ground color 

 flesh-colored with a bufnsh tinge. The postnuclear whorls are, in 

 addition to this, blotched, spotted, and streaked with chestnut-brown, 

 the spotting forming more or less of an interrupted median band. 

 The base also has an interrupted spiral band of dots about two-fifths 

 of the distance between the periphery and the umbilicus. The 

 malleations on the basal side are also darker tinged. The peristome 

 is flesh-colored with a dusky tinge, while the outer lip is a little darker 

 with the darker streaks of the outside showing through conspicu- 

 ously. In this subspecies we have an enormous variation both as to 

 size and the curving of the peripheral keel. In some individuals the 

 succeeding turns fall far below the peripheral keel and produce a 

 decidedly scalariform effect. The peripheral keel may jut out in a 

 perfectly straight fashion or it may be upturned at the edge. All in 

 all, there is a greater range of variation here than I have observed 

 anywhere else in the genus Obba. The nuclear sculpture consists of 

 fine incremental lines and microscopic spiral striations, while the 

 postnuclear whorls have the basal half malleated and the whole sur- 

 face marked by rather strong incremental lines and slender incised 

 spiral lines. In addition to this, there is a conspicuous crisscross 

 sculpture best developed on the last portion of the last whorl. The 

 base is somewhat inflated with rather feeble incremental lines and 

 moderately well-incised spiral striations. This also has malleations 

 between the brown band and the periphery, and is likewise provided 

 with a strong crisscross sculpture. The aperture is oval with the 

 peristome quite strongly expanded and reflected, covering about 

 one-third of the umbilicus. All our specimens are from the Island of 



Type. 



