Turritella from Buda and Georgetown Limestones 17 



The ornamentation of the whorls consists of five nodular 

 ribs, the posterior of which begins at the suture and the 

 rest follow at equal distances. The posterior rib is also 

 the largest, the others successively decreasing in size. The 

 anterior rib is rather narrow. 



Comparisons. This species is distinguished from Turri- 

 tella granulata, Sow., var. cenomanensis, D'Orb. by the size 

 of the apical angle, which is 15 in the latter species. In 

 our species the posterior rib begins immediately at the su- 

 ture, causing the whorl to be square-shouldered, whereas in 

 T. granulata, Sow., var. cenomanensis, D'Orb. the whorl has 

 two narrow bands, one slanting toward the posterior suture 

 and the other toward the anterior suture, causing the whorl 

 to be beveled instead of square-shouldered. 



Number of specimens. 1. 



Occurrence. From east side of Mt. Bonnell, Georgetown 

 limestone, Austin, Texas. 



Turritella bonnellensis, n. sp. 

 Plate IV, figures 5, 6 



Dimensions. Apical angle 17, sutural angle 13. 



Description. Shell is small, slender, whorls high, about 

 two-thirds as high as wide, side of whorls flat, whorls five 

 or more in number. Suture not well defined. Ornamenta- 

 tion consists of four equal nodular ribs, two posterior and 

 two anterior to the median line. In front of the anterior 

 pair of ribs there is a smaller nodular rib. Between the 

 pair of anterior ribs and the pair of posterior ribs there 

 is a broad excavation or depression slightly wider than the 

 space occupied by either pair of ribs. In this depression 

 there is a nodular rib with a fine nodular thread behind 

 it. In the older portion of the shell a nodular thread ap- 

 pears between the ribs. Ribs are close together. 



Number of specimens. 3 and a mould. 



Occurrence. Georgetown limestone, east side of Mt. 

 Bonnell and Shoal Creek, Austin, Texas. 



