TJie Fauna of the Ma.vviUe Limestone. 



397 



1909. Etioinphalus siviilis. Grabau and Shimer, N. A. Index Foss., pp>.. 

 «59, 660, 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 

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

 line to the suture. 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 strife. 



Fig. 22. — Straparollus 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 off from the median peripheral line of 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 



