92 STUDIES IN GEOLOGY, No. 3 



Turbo belli var. aequifilicatum n. var. 

 PLATE; IV Fig. 12. 



Shell turreted, the whorls distinct, angulated. Differs 

 from belli chiefly in sculpture, which consists of evenly 

 spaced major cords without the regular subsidiary threads. 

 On the last whorl of the spire one of the cords forms a keel, 

 behind which the surface is horizontal, bearing one less 

 prominent cord, and before which the surface is almost 

 vertical, bearing two prominent cords between the keel and 

 the suture. The body whorl bears many more ribs about 

 ten from the keel to the base of the columella. Just below 

 the keel on the body whorl is one subsidiary thread, and the 

 two on either side of the lowest prominent rib are less prom- 

 inent than the rest. In shape and other characteristics this 

 variety is similar to the restricted species. The dimensions 

 are therefore similar. 



Lower Zorritos. Quebrada Zapotal. 



Genus CALLIOSTOMA Swainson 



Calliostoma (Eutrochus) noduliferum Nelson 



PLATE I Figs. 7, 8. 



Calliostoma noduliferum Nelson, Trans. Conn. Acad., vol. 2, 

 p. 187, pi. 16, fig. i, 1870. 



Shell of medium size, spire moderately elevated, sutures 

 distinct. Whorls six in number, convex, evenly rounded 

 above. Sculpture of finely beaded spiral threads, six to the 

 whorl, the interspaces about twice as wide ; at the beginning 

 of the latter half of the body whorl interstitial threads 

 develop, beginning as very fine simple threads and gradually 

 becoming beaded, but remaining subsidiary in size. The 

 base of the body whorl is set off by a fairly sharp peripheral 

 keel, and is flattened to convex, with about twelve spiral 

 cords between the keel and the columella. Aperture sub- 



