62 Studies in Geology, No. 3 



does giippyi; it is still more delicate, and has a somewhat 

 greater apical angle. The ribs are subequal, the anterior, if 

 any, being more prominent in both guppyi and dicingula. 

 Lower Zorritos. Between Quebradas Heath and Charan. 



Turritella alturana n. nom. 



Plati; II— Fig. 3. 



Turritella plana Nelson, Trans. Conn. Acad., vol. 2, p. 188, 1870; 

 not of McCoy, nor of Brinkhorst, 1861. 



Shell large, heavy, "solid, the apical angle small and the 

 spire very high. Whorls, averaging 16 in number, pos- 

 sibly more, flat-sided, the earlier ones being set off merely 

 by a deep, sharp, L-shaped depression at the suture, and 

 the later ones having the semblance of a carina near the 

 base, the sutural depression being broader. In full grown to 

 gerontic specimens the body whorl and the penultimate are 

 rounded-convex, the surface being distorted by rough and 

 irregular growth-wrinkles. Sculpture of fine subequal 

 threads, about 17 in the space of 5 mm. on the later whorls 

 (not 25, as stated by Nelson), separated by still finer inter- 

 spaces. The threads coalesce occasionally, two or more 

 combining to form a group set off on either side by deeper 

 depressions. Broadly sinuate growth-lines are discernible 

 over the entire shell ; on the last two whorls of old specimens 

 they are magnified into irregular wrinkles. Length of frag- 

 ment bearing 71^2 lower whorls, 117 mm.; diameter of body 

 whorl, 29.25 mm. ; of uppermost whorl, 13.5 mm. Estimated 

 length of complete full-grown specimen bearing 17 whorls, 

 163 mm. 



Well-defined fragments of the anterior portion of this 

 species occur in a block of gray marl which was found on 

 the beach near Quebrada Tijeritas, north of Zorritos. Since 

 all three members of the Zorritos formation are exposed 

 within reasonable distance of the spot it is not safe to suppose 

 the origin of the material, and when the fact is considered 

 that the species is not typical of the American Miocene, but 



