22 THE GASTROPOD GENUS YVANIA 



inner edge of the slit band and the suture. They are here regularly convex 

 and sweep backward to join the edge of the band at an acute angle. Toward 

 the suture the growth lines extend in a sinuous curve, first convex but as the 

 suture is 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 arbitrarily bounded below by a 

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

 surface. This costa is narrow and angular and the slope upon the upper side 

 is somewhat steeper than upon the lower. Above this costa and separated 

 from it by a distance somewhat less than one third of the width of the lateral 

 surface is another similar or slightly more prominent costa. Above this to the 

 slit band the surface is flat or smooth with the exception of growth lines 

 which curve strongly backward and approach the border of the slit band at 

 an acute angle. Between the two costae on the lower part of the lateral slope 

 the growth lines are essentially normal to these markings. 



The basal surface of the whorl is ornamented by numerous revolving 

 costae separated from each other over the greater part by .2 mm. or less. 

 On the outer portion, however, they are more widely spaced, the first two 

 or three being separated from each other and the costa bounding the basal 

 surface by spaces about equal to or slightly less than that which intervenes 

 between the two costae of the lateral surface of the whorl. The costae of 

 the base do not extend down into the umbilicus. The holotype possesses 12 

 costae upon the basal surface. The growth lines are very slightly concave 

 in the central part of the basal surface, but as the umbilicus is approached 

 they become slightly convex. 



Remarks. — The species Yvania gurleyi is very closely related to Y. 

 inclinata from which it may be recognized by its slightly narrower slit band 

 bounded by less prominent costae, the coarser nature of its other markings, 

 the absence of fine costae upon the lateral surface of the whorl and of those 

 adjacent to the suture on the upper surface. 



The holotype of this species is No. 6351 in the collection of Walker 

 Museum at the University of Chicago. 



Occurrence. — This species was obtained in a beautifully pyritized con- 

 dition from the black shales which overlie the Danville coal near Danville, 

 Vermilion County, Illinois. 



Yvania supercrenata Weller, n. sp. 

 PI. I, figs. 2a-3; PI. Ill, fig. 8 



Description. — Shell small, somewhat higher than wide, slightly turreted, 

 spiral angle about 86° ; whorls angular, base convex, umbilicus small ; last 



