60 STUDIES IN GEOLOGY, No. 3 



Twritella altilira Conrad, Pac. R.R. Rept., vol. 6, pt. 2, p. 72, 

 pi. 5, fig- !9, i857- 



Not T. altilira Gabb, Jour. Ac. Nat. Sc. Phila., vol. 8, p. 34*. 

 pi. 44, figs. 9, 9a, 1877 (=T. sapotensis Brown and Pilsbry, loc. 

 cit, p. 359, PL 27, fig..io). 



Not T. altilira Grzybowski, Neues Jahrb., B.B. 12, p. 645, pi. 20, 

 fig. 7, 1899 (=-T. dicingula Woodring Ms. ) 



Turritella gabbi Toula, Jahrb. k.k. geol. Reichs., vol. 58, p. 695, 

 pi. 25, fig. 5, 1908. 



Turritella altilira Brown and Pilsbry, Proc. Ac. Nat. Sc. 

 Phila., vol. 63, p. 358, pi. 27, figs; 2, 3, 1911. 



"Subulate, carinated; volutions with 2 distant, elevated, 

 revolving, crenulated ribs, interstices with revolving lines; 

 body volution, bicarinated at the angle." Conrad, 1857. 



" It tapers slowly, and, judging from the broken speci- 

 mens seen, must attain a length of upwards of 100 mm., 

 with a basal diameter of 18 mm., and probably over 25 

 whorls. Each whorl bears two very high spiral ribs, cren- 

 ulated at their summits, the lower rib narrow, the upper 

 wider, usually but not always double at the ridge, or with a 

 lower cord below the main one. The deep concavity between 

 the ridges has sculpture of several unequal spiral cords, more 

 or less crenulated ; and the whole surface, when most perfect, 

 has a fine spiral striation. The last whorl has a third rib, 

 sub-peripheral in position, the base below it somewhat con- 

 vex, marked with some radial striae and lamellae. On the 

 early whorls the spiral ribs are less prominent and the inter- 

 stitial beaded cords are rather better developed. "Brown 

 and Pilsbry, 1911. 



In the Zorritos forms the upper rib is not double, but it 

 often bears the lower cord noted by Brown and Pilsbry. 

 The difference in width between the two prominent ribs is 

 not always marked. The crenulations are partially lost on 

 the ribs of the body whorl, and the interspace is more 

 rounded out, more gently concave. On most of the whorls 

 of the spire there is a fine indentation below the first cord 



