46 STUDIES IN GEOLOGY, No. 3 



all the Zorritos mollusks. It was referred by Nelson to the 

 genus Cuma, which has since been placed in synonymy with 

 Cymia, but it is obviously not of that genus. It is very close 

 to S. dalli Brown and Pilsbry, 39 from Gatun, differing from 

 that species in having a larger number of more closely spaced 

 primary threads, with the three orders of threads not as 

 prominently differentiated as in dalli; the sculpture on the 

 shoulder of the body whorl is not nearly as strong ; the base 

 is somewhat more produced, the canal and f asciole being 

 longer. The recent S. elegans is somewhat similar, but 

 differs in having heavier spiral threads, with the longitudinal 

 folds equally strong over the entire length of the whorl ; in 

 altemata they are stronger at the keel and subdued near the 

 suture. 



Lower Zorritos (Variegated?). South of Quebrada 

 Pantheon ; Quebrada Zapotal. 



Subfamily PHOTINAE 



Genus PHOS Montfort 



Phos (f) latirugatus n. sp. 



PLATE I Fig. 12. 



Shell of medium size, turreted, the spire high, the whorls 

 inflated. First neanic whorls unknown; the following 

 whorls fairly evenly convex ; at about the fifth whorl a keel 

 develops, and with the keel a series of longitudinal folds. 

 On the later whorls the shoulder set off by the keel becomes 

 more nearly horizontal, the keel becoming more nearly level 

 with the suture, and the longitudinal folds grow broader and 

 farther apart. At the juncture of the longitudinal folds and 

 the keel nodes exist. Spiral sculpture of two orders of 

 threads ; between the keel and the base on the body whorl 

 there are about n or 12 major threads which are more 

 closely spaced below ; between the major threads are almost 



Proc. Ac. Nat. Sc. Phila., vol. 63, p. 348, pi. 24, fig. 14, 1911. 



