32 THE GASTROPOD GENUS YVANIA 



appear upon the slope from the basal surface into the umbilicus, three or 

 four of these having been observed upon one specimen. Lines of growth 

 upon the base are broadly and gently concave and have a slight backward 

 sweep, becoming slightly convex in the umbilical area. 



Remarks. — The species Yvania adamsi is most closely related to Y. 

 salinensis, from which it may be distinguished by the less acute spire, the 

 flatter base, the more concave lateral slope and the double costa which marks 

 its lower limit, the less prominent suture, and the general trochiform shape. 



The holotype of this species is catalogued as No. 2536 in the paleon- 

 tological collection of the Illinois State Museum. A substitution of speci- 

 mens has however apparently taken place for the specimen bearing this 

 number is not Y. adamsi and the type of this species has not been located. 



Occurrence. — This species is typically developed in the Lonsdale lime- 

 stone. It is present in many collections from this horizon but the preserva- 

 tion is very rarely such that the details of the external features may l)e noted. 

 The specimens illustrated on Plate II are from the NW. Y\ sec. 34, T. 8 N.. 

 R. 6 E., Peoria County, Illinois. The exact locality from which the type of 

 this species was obtained is unknown. 



Yvania subconstricta (Meek and Worthen) 

 PI. II, figs. 4a-5c; PI. Ill, fig. 10 



1860 Plcurotomaria subconstricta. Meek and Worthen, Acad. Nat. Sci. Phil., 

 Pr. p. 458. 



Coal Measures : Hodge's Creek, Macoupin County, Illinois. 



1866 Pleurotomaric subconstricta. Meek and Worthen, Geol. Survey of 

 Illinois, vol. 2, p. 351, PI. 28, figs. 6a-c. 



Lower Coal Measures : Hodge's Creek, Macoupin County, Illinois. 



Description.- — Shell small to medium sized, higher than wide, subtrochi- 

 form to slightly turreted. spiral angle about 60° to 70° ; whorls angular, base 

 convex, not umbilicated ; last whorl forms a little more than half the height 

 of the shell ; surface marked by numerous revolving costae which are nodose 

 adjacent to the suture, and by transverse lines of growth ; slit band prominent, 

 flat, located on the upper sloping surface of whorl and adjacent to the angle. 



The dimensions of an average specimen are: height of entire shell 

 7.4 mm.; height of last whorl 4.2 mm.; and width at base 6.1 mm. This 

 specimen is composed of about seven whorls. Another individual, the 

 largest one that has been obtained, has the following measurements : height 

 of entire shell 12.6 mm. ; height of last whorl 7.4 mm. ; and width at base 

 8.9 mm. It is made up of about eight whorls. The first three turns of the 

 spire are uniformly convex. The first two are coiled in a practically flat 

 spiral but thereafter the spire is uniformly developed. Upon the third whorl 



