490 Systematic Paleontology 



Description. — " Turrited ; whorls with three equidistant, very acute, 

 prominent ribs; revolving lines microscopic, closely arranged." — Conrad, 

 1860. 



Type Locality. — Tippah County, Mississippi. 



Shell turrited, large for the genus, attaining a maximum altitude of 

 ± 80 mm. and a diameter of more than 20 mm. ; whorls probably sixteen 

 or more in number in a perfect individual, the earlier whorls flattened, the 

 later feebly convex, converging at an angle of about 25° ; external surface 

 sculptured with three sharply and very prominently elevated laminar 

 equisized and equilateral ridges, separated by symmetrically concave inter- 

 spaces, the posterior spiral a little nearer the suture line than the anterior ; 

 interspiral areas threaded with miscroscopically fine lira?, which are 

 minutely crenulated by the incrementals ; suture lines distinct, impressed 

 but inconspicuous by reason of the overhanging spiral ridges placed about 

 midway on the upcurve of the interspiral between the posterior lamina 

 and the anterior lamina of the preceding turn ; interspiral areas between 

 the lamina? of succeeding whorls scarcely wider than those between the 

 lamina; on the same whorl ; base very finely and evenly threaded ; casts 

 characterized by evenly rounded whorls, separated by rather deep sutural 

 channels. 



In a single individual from Brightseat which is doubtfully referred to 

 this species the posterior of the three spirals is much less elevated than 

 the two in front of it. The general contour of the shell, the character of 

 the secondary sculpture and the position of the suture line are normal for 

 the species, and it is impossible to determine the significance of the vari- 

 ation in the primaries without further material. 



Occurrence. — Matawan Formation. Arnold Point on the Severn 

 River, Ulmstead Point, Magothy River, Anne Arundel County. Mon- 

 mouth Formation. Brightseat, Brooks estate near Seat Pleasant, 

 ? Friendly, McNeys Corners, Prince George's County. 



Collections. — Maryland Geological Survey, New Jersey Geological Sur- 

 vey, U. S. National Museum. 



Outside Distribution. — Matawan Formation. Wenonah Sand, New 

 Jersey. Blade Creek Formation. North and South Carolina. Peedee 



