THE GASTROPOD GENUS YVANIA 35 



costa and bears upon its surface three or less commonly four more. These 



costae are not quite as prominently developed as the one along the lower 

 boundary of the lateral slope and are somewhat more closely spaced on the 

 upper portion of this surface. Where the fourth costa is present it is very 

 tine and is located just below the angle. These costae are rounded and the 

 interspaces are gently concave to flat. Lines of growth are conspicuous on 

 this portion of the shell. They cross the lowest bounding costa at about 

 right angles hut just above it they bend sharply forward and traverse the 

 -• interspace in a diagonal direction: in the second interspace they are ap- 

 proximately vertical hut swing strongly backward on the remainder of the 

 lateral slope and meet the edge of the slit hand at an acute angle. The growth 

 lines are conspicuous only in the interspaces and are not visible crossing 

 the revolving costae except for slight irregularities which they produce. 



The basal surface carries about eleven rounded spiral costae separated 

 by concave interspaces. The costae are rather uniformly spaced except in 

 the region of the columella where the spaces are somewhat narrower. A 

 few specimens show the outer costae as well as the inner spaced somewhat 

 more closely than those which occupy the central part of the basal surface 

 of the whorl. Lines of growth are fairly distinct. From the outer angle 

 they sweep very gently backward in a broad shallow concave curve to the 

 middle part of the basal surface; on the inner portion a slight convexity is 

 (leveloj>ed in the vicinity of the columella. 



Remarks. — The species Yvania subconstricta is closely related to Y. 

 giffordi from which it may he distinguished by its less acute spire, the wider 

 slit hand, and the horizontal area adjacent to the suture. 



The holotype of this species is preserved in the paleontological collection 

 at the University of Illinois. 



Occurrence. — This species was originally described from an outcrop of 

 the limestone which underlies the Belleville (No. 6) coal on Hodges Creek 

 in the SW. % sec. 30. T. 10 X.. R. 9 \\\. Macoupin County, Illinois. It 

 has subsequently been collected from the same horizon in Greene County, the 

 limestone cap rock of the Herrin (No. 6) coal in Saline and Gallatin Conn- 

 tie-. Illinois, the Piasa limestone in St. Louis County, Missouri, and from 

 the Lonsdale limestone in Peoria County, Illinois. This stratigraphic range 

 i- greater than has been observed for any of the other species of Yvania in 

 our Coal Measure- strata. Most of the other s]>ecies. so far as is known at 

 present, are confined to a single horizon, hut future investigation will probably 

 reveal that each of these also occurs in other neighboring horizons. 



Since this paper was prepared a representative of this species has been 

 recognized in a collection made from the Drum lime-tone at Kansas City. 

 Missouri, during the summer of 1928. 



