20 THE GASTROPOD GENUS YVANIA 



tion. Its chief points of difference are the relatively narrower slit band and 

 the conspicuous outward sloping of the lateral surfaces of the whorls. In 

 its ornamentation the species under discussion is intermediate between the 

 other two. It is, however, more closely related to Y. inclinata than to Y. 

 gurleyi. 



The holotype of this species is No. 7 in the collection of the Illinois 

 State Geological Survey. 



Occurrence. — This species occurs in a silicified condition in a dark lime- 

 stone near the base of the Pennsylvania!! in the NW. *4 sec - 35, T. 21 N., 

 R. 9 W., Warren County, Indiana. 



Yvania gurleyi (Meek) 

 PI. Ill, figs, la-d, 7 



1871 Plcurotomaria gurleyi. Meek, Acad. Nat. Sci. Phil., Pr. p. 117. 

 Coal Measures : Danville, Illinois. 



1873 Plcurotomaria Gurleyi. Meek and Worthen, Geol. Survey of Illinois, vol. 



5, PI. 30, figs. 6a, b. 

 Coal Measures. 



1874 Plcurotomaria Gurleyi. Meek, Am. Jour. Sci. (3) vol. 7, p. 584. 



Description. — Shell small, slightly turreted, spiral angle about 92°; 

 whorls angular, base convex, umbilicus small ; last whorl forms over half the 

 height of the shell ; surface marked by numerous revolving costae ; slit band 

 prominent, concave, slightly inclined to the upper sloping surface of the whorl 

 and adjacent to the angle. 



The dimensions of the holotype are : height of the entire shell 5.8 mm. ; 

 height of the last whorl 3.2 mm. ; and width at base 5.4 mm. It is composed 

 of five and three quarters whorls. The first turn is practically flat, the second 

 is very low, and it is only in the later ones that the elevated spire is developed. 

 The first two and one half whorls are uniformly convex. In the next the 

 angularity appears and rapidly attains mature development. No markings 

 are observed upon the surface of the first whorl. On the second whorl there 

 appear a number of indistinct revolving striae. At the beginning of the third 

 turn these resolve themselves into a series of seven, approximately equally 

 prominent and equally spaced revolving costae. The space between the 

 second and third of these, counting outward from the suture, is occupied 

 by the slit band. Early in the third turn this area becomes wider, and another 

 revolving costa appears between the suture and the first costa previously 

 visible. In the latter part of the third turn the costa bordering the slit band 

 becomes relatively more conspicuous whereas the first one on the lateral 

 surface below the band and the first one above it on the upper surface become 

 very faint and shortly become obsolete. Also the lowest costa upon the lateral 



