130 BULIMULUS-BOSTRYX-ATAXUS. 



This species is so excessively peculiar that comparisons with other 

 forms would be superfluous. The specific name given by Philippi 

 is preoccupied for another species belonging to Lissoacme, a closely 

 allied section of this genus. This duplication arose from the refer- 

 ence of the present form to the genus Helix. 



Section 2. ATAXUS Albers, 1850. 



Ataxus ALB., Die Hel., p. 164 (only species B. umbilicaris Soul.). 



Shell elongated, ovate-conic or subfusiform, with numerous (7-9) 

 rather flattened whorls ; umbilicus very large, deep and well-like, 

 with subperpendicular walls ; aperture small. Type B. umbilicaris 

 Soul. 



Distribution, northern Chili and Andean plateau of Peru. 



Key to species of Ataxus. 



a. Shell smooth or nearly so, conic ; umbilicus extremely large, 



umbilicaris. 



aa. Shell striated, fusiform ; umbilicus smaller. 



b. Aperture over one-third the alt. of shell, infundibulum. 

 bb. Aperture less than one-third the alt. of shell, 



umbilicatellus, 



aaa. Surface of shell ribbed. 



b. Surface costulate, tubulatus. 



bb. Surface distantly ribbed, like a Scalaria, scalaricosta. 



B. UMBILICARIS Souleyet. PI. 44, figs. 87, 88. 



Shell with ample, well-like umbilicus, long-conic; thin but rather 

 solid ; opaque, white or flesh-tinted ; smooth except for slight 

 growth-lines usually indistinctly crimped in spiral order, shining. 

 Spire attenuated above, the earlier whorls smooth, corneous, mamil- 

 lar. Whorls 7, slightly convex, regularly widening, tfte last not de- 

 flexed, narrowed toward the base, forming a narrowly rounded ridge 

 around the very large umbilicus, which penetrates well-like to the 

 apex. 



Aperture small, oblique, narrowly oblong ; peristome white, sub- 

 continuous, in contact with the body-whorl only for an extremely 

 short distance above ; outer and basal lips narrowly expanded, col- 

 umellar lip straighter, dilated. 



Alt. 15, diam. 7 mill. ; alt. of aperture 6'6 mill. 



Alt. 14'3, diam. 6 mill.; alt. of aperture 5 mill. 



Alt. 12'7, diam. 7 mill. ; alt. of aperture 5 mill. 



Cobija, northern Chili. 



