Paleontology Zorritos Formation 85 



Die Umgange sind stark conisch, unten stark gekielt, 

 zwischen dem Kiel und der flachen Xaht concav eingesch- 

 niirt. Die Oberflache tragt iiber dem Kiel 5, unter demselben 

 I flache Leiste. Die Hohe der 2 unteren Umgange 45 mm., 

 Breite unten 35 mm., oben, 23 mm. ; die totale Lange mag 

 140 mm. betragen." — Grzybowski, 1899. 



The keel is very sharp and attenuate, forming a knife- 

 like edge, and giving the shell something of the appearance 

 of an Archimedes spiral. Four of the threads above the 

 keel are always strong, and the one nearest the keel is some- 

 times distinctly weaker. In some specimens this thread Is 

 obsolete, and there is an additional thread above. In the 

 earlier whorls the suture is always indistinct, and in some 

 specimens it is not marked on all of the whorls, but others 

 show a plane-bottomed projection of the base of the lower 

 whorls which indicates clearly the position of the suture. 

 This overhanging base is developed to varying degrees of 

 strength. Lines of growth are clearly visible. Length about 

 100 mm. or more; diameter at base, 31 mm. 



This species is a striking form of a type which is appar- 

 ently not known on the Atlantic Coast outside of the Eocene, 

 but which appears in the Miocene of California. It is ver\' 

 close to T. ocoyana Conrad," from the Lower Miocene of 

 California, from which it dififers chiefly in having a sharper 

 keel. 



L'pper Zorritos. Quebrada del Toro. 



Turrit ella robusta var. abrupta n. var. 



Plate IV— Fig. 6. 



Shell essentially similar to T. robusta in all characters 

 save the sculpture, which consists of closely set cordate ribs 

 instead of separated threads. There are about eight of these 

 cords above the keel and three below. The anteriormost 

 precarinal cord borders the suture, which is everj-where in- 



Pao. R.R. Rept., vol. 5, p. 329, pi. 8, figs. 7^, 73a, D, 1856. 



