36 STUDIES IN GEOLOGY, No. 3 



spiral ribs instead of 14, and in the less prominent threads 

 on the band ; otherwise it is identical. It differs from the 

 variety foevifasciola Maury, from Santo Domingo, 21 in its 

 larger number of longitudinal ribs, and in the presence of 

 vestigial spirals on the fasciole. The absence of such spirals 

 is apparently the only point of difference between laevifas- 

 ciola and gausapata. 



Lower Zorritos. Hervideras, Zorritos district. 

 Terebra tuberosa (Nelson) 

 PLATE I Fig. 2. 



Myurella tuberosa Nelson, Trans. Conn. Acad., vol. 2, p. 193, 

 i8;d. 



"Shell turreted, slender and acuminate; whorls eight to 

 ten, depressed or slightly concave, except the body whorl; 

 sutures indistinct. Cincture broad, elevated, with obtuse 

 tubercles, not as wide as the spaces between them. Longi- 

 tudinal ribs distinct. Whorls marked by from four to six 

 nearly equal transverse ridges, which rise into strong tuber- 

 cles over the ribs, x x x " Nelson, 1870. 



The spiral sculpture consists of six bands on the main 

 part of the whorl, separated by narrow interspaces. The an- 

 teriormost of the spiral bands is usually not prominent, and 

 is sometimes occluded by encroachment of the fasciole. The 

 longitudinal sculpture consists of a series of raised ridges, 

 about 14 on a whorl, which are prominent on the fasciole, 

 giving it the appearance of a worn cog-wheel. On the main 

 surface of the whorl the ridges are more subdued, but still 

 distinct, raising the spiral bands into the tubercles noted by 

 Nelson. Usually one or more of the longitudinal ribs on 

 each whorl is bifid at the summit. Lines of growth cross 

 all parts of the whorl. The base is sculptured with spiral 

 bands similar to those on the main body of the whorls, the 

 continuation of the area covered by the fasciole being 



21 Bull. Amer. Pal., vol. 5, No. 29, p. 27, pi. 3, fig. 19, 1917. 



