Paleontology Zorritos Formation 8i 



fifteen in number. Sculpture of seven subequal spiral 

 threads, with no distinct subsidiaries. Occasionally an eighth 

 thread is visible at the extreme base of the whorl, margin- 

 ating the suture. The anterior three of the seven threads 

 normallv visible are equally spaced : between the third and 

 fourth the space is smaller, and the fifth and sixth are very 

 close together, with the seventh about as far from the sixth 

 as the fourth is from the fifth. This spacing is common, 

 but rare forms have the threads more nearly equally spaced, 

 excepting the fifth and sixth, which are constantly proxi- 

 mate. Subsidiary threads occur but rarely, and then indis- 

 tinctly. A hint of an additional posterior thread, very fine, 

 is present on one specimen. The subcarinal subsidiaries 

 normally present in infracarinata s.s. are only suggested in 

 this variety. The form of the whorls is convex, rounded, 

 with no distinct carina. The point of greatest whorl-diam- 

 eter is at the position of the carina in the angular infracarin- 

 ata, but a sharp carina is never present, and the supracarinal 

 surface is always covex, if only slightly so in some speci- 

 mens. Length of fragment showing the body whorl and 

 23^ on the spire, 59 mm. ; maximum diameter. 24 mm. Di- 

 mensions of complete shell probably similar to those of 

 infracaritiata. 



Upper Zorritos. Quebrada del Toro. 



TurritcUa prenuncia n. sp. 

 Plate IV— Figs. 1-3. 



Shell small, delicate, the apical angle moderate, whorls 

 fairly tight-coiled, sutures distinct. There appear to be 

 two types of early development, each of which attains the 

 same end result in the fully mature whorls, but which are 

 sufiicientlv diflferent in the neanic whorls to deserve notice. 

 The two types are here described separately, being noted, for 

 convenience in reference, as (a) and (b). 



(a). Protoconch bulbous, consisting of one and a half 

 turns. Xeanic whorls carinate, strongly sculptured by cor- 



