THE GASTROPOD GENUS WAN I A 25 



Remarks. — The species )':\uiiii supercrenata is very closely allied to )'. 

 knight i from which it may be distinguished l>y its relatively narrower hand, 

 the more numerous revolving costae above the hand, the greater prominence 

 of the costa adjacent to the suture, the ornamentation which may occur upon 

 the hand, the less prominent costa upon the outer border of the hand, the 

 lesser concavity of the smooth area just below it, the more convex basal 

 surface, the presence of a well formed umbilicus, the more equal spacing of 

 the costae of the hasal surface, and the uniform enlargement of the whorl 

 resulting in a more regular spire. 



Yvania supercrenata may he distinguished from )'. inclinata with which 

 it is associated by its slit hand which lies in the plane of the upper surface 

 of the whorl, the flatness of the upper surface, the higher spire, the fewer 

 and coarser revolving costae, and the less uniform spacing of the costae 

 upon the hasal surface. 



The holotype of this s]>ecies is No, 1 in the collection of the Illinois 

 State Geological Survey. 



Occurrence. — This species occurs in a limestone bed which closely under- 

 lies the Colchester (No. 2) coal over large areas in western Illinois. The 

 holotype and a series of other s]>ecimens were collected from an outcrop in 

 the northeast hank of Wilson Creek near the southwest corner sec. 26, 

 T. 3 X., R. 2 E.. Fulton County, Illinois. 



Yvania knight] Weller, n. sp. 



PI. I, figs. 5-8; PI. Ill, fig. 9 



Description. — Shell small, higher than wide, turreted, spiral angle about 

 75 : whorls angular, base slightly convex, umbilicus closed; last whorl forms 

 less than half the height of the shell ; surface marked by numerous revolving 

 costae; slit hand prominent, concave, located on upper flattened surface of 

 whorl and adjacent to the angle. 



The dimensions of the holotype are: length of entire shell 7.6 mm.; 

 height of last whorl 3.3 mm.; and width at base 6.4 mm. This specimen is 

 composed of seven whorls, the first four of which are uniformly convex. 

 The early ones are smooth hut at the beginning of the fourth turn four re- 

 volving co>tae are conspicuously developed. These are of about equal size, are 

 uniformly spaced, and the second and third enclose the area of the slit hand. 

 During the course of the fourth turn the characteristic mature angulation 

 develops, due principally to the more prominent development of the costae 

 which hound the hand. The interspace below the hand increases somewhat 

 in width hut the upper slope of the whorl remains divided into three areas 

 of almost equal width until in the course of the sixth turn the interspace 

 above the hand becomes relatively wider and there appears upon its surface 



