PALEONTOLOGY ZORRITOS FORMATION 57 



ture unknown. Height of fragment bearing 4^ whorls, 

 58.5 ; maximum diameter, 27 mm. 



The sculpture of the lower whorls of C. infranodatum is 

 similar to that of C. nodulosum Bruguiere, 51 the type of 

 Cerithiuni s.s., a group not known fossil. The sculpture of 

 the earlier whorls recalls somewhat that of C. grillanum of 

 the Zorritos fauna. The species is characterized by 

 the marked difference in sculpture shown by the earlier and 

 later whorls. 



Upper Zorritos. Quebrada del Grillo. 



Cerithium grillanum n. sp. 

 PLATE II Fig. 10. 



Shell small to medium-sized, highly ornate. Whorls prob- 

 ably eight to ten in total number. Sculpture of transverse 

 nodes crossed by spiral cords ; on the earlier whorls the nodes 

 are long and undifferentiated, appearing in worn specimens as 

 cogs ; on the later whorls of the spire they are differentiated 

 into two series through the swelling laterally of their upper 

 and lower parts, and not through mesial sulcatlon ; the upper 

 of the two series gradually becomes the more prominent 

 until on the body whorl the lower nodules are almost obsolete, 

 and three additional rows of nodules, really nodulate spiral 

 straps, appear on the basal surface. There is some varia- 

 tion in the differentiation of the nodules ; on some speci- 

 mens the upper series gains the ascendancy well up on the 

 shell, whereas in others the rows are subequal until the 

 penultimate whorl. In specimens which show early differ- 

 entiation of the two series of nodes the lower series contains 

 more nodes than the upper. A series of fine spiral cords, 

 which are weaker on the nodes, covers the whorls. On the 

 base of the body- whorl there are two or three cords between 

 the noded straps ; thence upward they are similarly distri- 



51 Cossman, Ess. Pal. Comp., vol. 7, p. 66, pi. 3, fig. 10, 1906. 



