THE GASTROPOD GENUS WANIA 37 



lower position so that a narrow strip of the basal surface of the preceding 



whorl remains visible. 



The dlumellar lip is strongly recurved upon itself and considerably 

 thickened. It extends over and in most cases completely closes the umbilicus. 

 There is no thickening or callosity developed upon the inner lip. 



The slit hand is located along the outer margin of the upper sloping 

 •portion of the whorl and occupies a /one somewhat less than a half but 

 Usually more than a third of the width of the surface between the angulation 

 along its outer border and the angulation adjacent to the suture. The slit band 

 is essentially flat and is bounded by two low narrow angular costae. Its 

 surface is covered by numerous tine crescentic transverse costae which are 

 - j though irregularly Spaced. They are asymmetrically curved, the great- 

 est concavity occurring above the middle of the band so that they meet the 

 outer edge in a position somewhat more advanced than that of their junction 

 with the inner boundary. No revolving ornamentation is present upon the 

 slit band. 



The most conspicuous costa upon the upper surface of the whorl occurs 

 upon the angle adjacent to the suture. Below this angle and above the costa 

 which marks the inner side of the slit band occur or. most specimens two 

 additional costae which become obsolete in the gerontic stage in the growth 

 of the shell. The narrow flat horizontal area adjacent to the suture is about 

 two thirds as wide as the slit band. Lines of growth are well developed 

 upon the upper surface of the whorl. < »n the narrow flat area adjacent to 

 tile suture they extend sharply backward, curve into a small sinus and join the 

 suture at nearly right angles. The lines of growth on this portion of the 

 shell may be somewhat grouped and form low rounded transverse ridges. 

 Upon the sloping portion of tin.- upper surface the growth lines are linguli- 

 form. reaching their most forward position slightly above the middle, from 

 which they sweep backward to the upper angulation and more strongly to 

 the border of the slit band which they meet at a very acute angle. The nodose 

 character of the costa occurring on the angle adjacent to the suture is asso- 

 ciated with the growth markings, but where growth lines cross the lower 

 costae only minor irregularities occur. 



The lateral slope of the whorl i- from two to two and one half times 

 as wide as the slit band. It is bounded below by a broad rounded costa and 

 bears upon its surface two or three smaller costae that are commonly liner 

 and more closely spaced toward the upper border. These costae are rounded 

 and the interspace- are gently concave to Hat. Lines of growth are con- 

 spicuous on this portion of the shell. They cross the lowest bounding costa 

 at about ri;dit angles but just above it they bend sharply forward and traverse 

 the first interspace in a diagonal direction: in the second inter-pace they 



