16 THE GASTROPOD GENUS VVANIA 



costa which marks the beginning of the curvature into the basal surface of 

 the preceding whorl. 



The columellar lip is blunt and recurved upon itself but not greatly 

 thickened. It extends over and almost completely hides a very small um- 

 bilicus. No thickening or callosity is present upon the inner lip. 



The slit band is situated along the outer margin of the upper sloping- 

 portion of the whorl and is inclined slightly downward from its general direc- 

 tion. The band is equal in width to slightly less than one fourth of the 

 complete width of the upper surface of the whorl and is bounded by two 

 prominent costae having angular or narrowly rounded crests whose converg- 

 ing slopes give to the band a concave outline. No ornamentation is present 

 upon the surface of tbe slit band in the mature portion of the shell. Lines 

 of growth are indicated by a few scattered, very faint, crescentic lirae which 

 are slightly asymmetrically curved so that each one touches the outer of tbe 

 bounding costae at a position a little farther to the rear than that at which it 

 touches the inner. 



The two costae which border tbe slit band are the most prominent mark- 

 ings upon the upper surface of the whorl. A third somewhat less conspicuous 

 costa parallels the suture and is separated from it by a distance about equal 

 to the width of the band. The space between this costa and the band is 

 slightly concave and is marked by as many as seven fine thread-like costae, 

 somewhat unequally spaced and in general alternating in size between fine 

 and very fine. A single fine costa occurs midway between the suture and the 

 more prominent costa mentioned above. Lines of growth are well developed 

 upon the upper surface of the whorl and are displayed by slight unevenness 

 of the shell surface. They are linguliform and attain their most advanced 

 position at about the midline of this part of tbe whorl. They are here regu- 

 larly convex and sweep backward to join tbe edge of the band at a sharp 

 angle. Toward the suture the growth lines extend in a sinuous curve, first 

 convex, but as the suture is closely approached the curve becomes slightly 

 concave, and they join the suture in a direction nearly normal to it. 



The lateral slope of the whorl below the outer edge of the slit band is 

 nearly as wide as the upper slope. It is bounded below by a conspicuous 

 costa which marks the beginning of tbe curvature into the basal surface. 

 This costa is broad and angular or narrowly rounded, the two slopes being 

 of about equal intensity. Above this costa and separated from it by a distance 

 somewhat less than one third of the width of the lateral surface is another 

 slightly less prominent costa of similar character. Midway between them 

 occurs a third finer costa. The surface between the angle of the whorl and 

 the second costa mentioned above is about equally divided into two parts. 

 The upper is without revolving markings and the lower is ornamented by 



