74 Studies in Geology, No. 3 



prominent threads, with interstitial threads barely percep- 

 tible. The chief point of difference lies in the less promin- 

 ent band. Length of fragment bearing the five anterior 

 whorls, 67 mm. ; maximum diameter at base, 22.5 mm. 



The differentiation of the variety trita from the typical 

 inca in the absence of abundant material has been a matter of 

 some deliberation ; but as matters stand the differences shown 

 by the form here proposed are too clear to permit its entire 

 identification with Grzybowski's species. T. (Haustator) 

 triplicafus var. dertosimplex Sacco,**® from the Miocene of 

 Europe, is closer to trita, apparently, than to the inca figured 

 by Grzybowski ; the comparison drawn by him places inca 

 midway between the varieties dertosimplex and superneapli- 

 cata of Sacco's triplicatns, and reference to Sacco's figures 

 shows some of the characteristics of trita to be susceptible 

 of similar placing. Observations such as that give rise to 

 the doubt concerning the identity of inca. Under present 

 circumstances, however, the best course seems to be to 

 retain trita as separate, particularly since the strength of the 

 upper carina, the dividing point, is constant in both the 

 Italian forms. 



Upper Zorritos. Quebrada del Toro. 



Tiirritella nelsoni n. nom. 



Plate III — Figs. 5, 6. 



Turritclla suturalis Nelson, Trans. Conn. Acad., vol. 2, p. 188, 

 1870, (ex parte) ; not of Sowerby, nor of Phillips. 



Young shell small, delicate. Whorls tightly coiled, the 

 apical angle moderate. Xeanic whorls characterized by prom- 

 inence of two subcentral threads which set off a band similar 

 to that characteristic of the adult T. inca, but situated farther 

 back on the whorl ; in the first two neanic whorls these two 

 threads are the only ones discernible, but on the third whorl 

 a faint subsidiary thread appears below the band and near 



Piemonte, pte. 19. p. 27, pi. 2, fig. 3^, 1895. 



