Tlic Fauna of the Maxi'illc Limestone 



397 



1909. liuoiii/^haliis siiiiilis. (;ral)au and Shinier, X'. A. Index Foss., pp.. 

 ()59, ()()(), fig. 909. 

 St. Louis: Illinois; Maxville, Ohio; Batesville, Arkansas. 



Description. — Shell varies from smaller than medium to> 

 medium size, .subdiscoidal or with a slightly elevated spire, and 

 with a broad umbilicus. Whorls about four in number and 

 gradually increasing in size. Whorls flattened on the upper sur- 

 face with a sharp keel on the peripheral angle, abruptly descend- 

 ing from the keel to the median periphery and then gently 

 roimded to the median basal line, and rounded from the latter 

 line to the sutinx. A sharp angular keel occurs on the median 

 basal line of at least the body whorl. Surface of the shell cov- 

 ered with closely crowded transverse strije. 



Fig. 22. — Siraparollits siiiiilis. 



a, b, and c. — Lateral, apical, and basal views of an individual, 

 (After Whitfield.) 



Diameter 14 to 25 mm. 



The shell is readily distinguished by its subdiscoidal outline, 

 large umbilicus, flattened upper surface of the whorls, the keels 

 of the upper and lower surfaces, and the crowded transverse 

 striae. 



Most of the specimens have a horizontal lateral extension, 

 which is given ofif from the median peripheral line (jf the last or 

 body whorl. This extension always adheres more or less to 

 the matrix and seems to be due to vertical crushing. 



It is one of the four most abundant forms of the Maxville 



