18 University of Texas Bulletin 



Turritella planilateris Conrad 



Turritella planilateris Conrad, Mexican Boundary Report, 

 p. 158, PI. 14, fig. la, b 



Plate IV, figure 7 



Description. Shell large, sides of whorls rounded, suture 

 well impressed. Ornamentation consists of four nodular 

 square ribs separated by a wide space. A nodular thread 

 occupies the space between the two middle ribs. 



Our specimen is only an external mould. 



Occurrence. Georgetown limestone east of Mt. Bonnell, 

 Austin, Texas. 



Turritella mabriensis, n. sp. 

 Plate IV, figure 8 



Dimensions. Apical angle 28, sutural angle about 8. 



Description. Shell is conical, stout, suture well im- 

 pressed, aperture rounded. The whorls, four or five in 

 number, are convex. They slope abruptly toward the an- 

 terior suture, and very gently toward the posterior suture. 

 The ornamentation of the whorls consists of five or six 

 nodular ribs with an intermediate nodular thread between 

 the fourth and fifth ribs from the anterior side. In front 

 of the anterior rib are two nodular threads. In addition to 

 these markings there are lines of growth. 



Only casts of this species have been found. 



Number of specimens. 14 casts. 



Occurrence. Georgetown limestone, near Camp Mabry, 

 T & G. N. R. R. cut, and Barton Creek, Austin, Tex. 



