Paleontology Zorritos Formation 87 



than is abnipta. It is different, however, in that its sculp- 

 tural threads are more nearly equal in strength, and 

 that its keel overhangs the suture more sharply than in 

 ocoxana. 



Lower Zorritos. Ridge between Quebradas Heath and 

 Charan. 



Family XATICIDAE 



Genus Polynices Montfort 



Polyniccs subangulata Xelson 



Plate IV— Fig. 8. 



Polyniccs subangulata Xelson, Trans. Conn. Acad. Sc, vol. 2, 

 p. 195, pi. 6, figs. 4, 12. 13, 1870. 



"Shell varies from obliquely oval to sub-globular, moder- 

 ately heavy and ventricose : spire short and pointed : body 

 whorl large, nearly seven-eighths of the length of the shell, 

 convex, slightly produced anteriorly, broadest about one- 

 fourth from top. From this point the whorl slopes, becom- 

 ing very much flattened and presenting a marked angular 

 appearance. Surface marked by distinct but irregular lines 

 of. growth. Sutures quite indistinct, except when the epi- 

 dermis is slightly worn off. Aperture semi-lunular. half as 

 wide as long, broadest a little below the middle. Outer lip 

 sharp and thin. Columellar lip covered by a very thick 

 callus, which rises into a more or less prominent ridge at the 

 broadest part of the shell. Umbilicus small ; in most speci- 

 mens reduced to a mere chink by the callus, which is pro- 

 longed below." — Xelson, 1870. 



The male shells and the young are more evenly rounded 

 than the mature females, which have the shoulder more 

 prominent, and in which the body whorl has a subcylindrical 

 shape. The callus widens above, merging with the inner 

 wall of the body w'horl a short distance behind the peristome 

 at its inner margin, and meeting the peristome exactly at its 



