66 STUDIES IN GEOLOGY, No. 3 



In addition to the fine sculpture noted by Grzybowski 

 there are four raised spiral ribs on each whorl, somewhat 

 similar to the basal keel, but much more subdued. The 

 anterior three of these ribs are equally spaced, but the space 

 between the fourth and the third is smaller than the others. 

 The alternation of strong and weak threads in the finer 

 sculpture, noted by Grzybowski, is best seen under the micro- 

 scope. The subsidiary sculpture covers the keel and ribs, 

 but opens out somewhat in their surfaces. The shell tapers 

 slowly; Grzybowski's figure suggests an apical angle larger 

 than that common to the species. Length of fragment 

 bearing 5^ whorls, 54.5 mm. ; diameter of body whorl, 17.5 

 mm. ; diameter of 6th whorl, 9.5 mm. 



This species differs from T. bifastigata Nelson, of the 

 Upper Zorritos fauna, in its development of but one sutural 

 keel or shoulder, and in its more regular sculpture. In 

 filicincta the stronger keel is at the posterior margin of the 

 whorl ; in bifastigata the reverse is true. T. filicincta differs 

 from its variety varicosta in its greater regularity of sculp- 

 ture and comparatively more prominent keel. It differs from 

 T. alturana; of the Zorritos fauna, in the possession of a 

 keel, and in its diversification of sculpture. T. megalobasis 

 Dall, 64 from the Orthaulax bed at Ballast Point, Florida, is 

 similar in sculpture and general appearance, but its apical 

 angle is far larger, and its keel is not as prominent. 



Lower Zorritos. Between Quebradas Heath and Charan. 



Turritella filicincta var. varicosta n. var. 

 PLATE III Fig. 3. 



This variety differs from T. filicincta in having a larger 

 number of primary ribs, irregularly arranged, and in having 

 a somewhat less prominent keel. One specimen only is in the 

 collection, and it is somewhat worn, with the subsidiary 

 sculpture not altogether clear; but it appears to agree with 



"Trans. Wag. Inst., vol. 3, pt. 2, p. 310, pi. 17, fig. n, 1892. 



