PALEONTOLOGY ZORRITOS FORMATION 79 



thread at the suture. These pre-carinal threads are weaker 

 in some specimens. Threads of the fourth order are very 

 fine and closely spaced, occurring over the entire length of 

 the whorl. The main thread is covered with these quaternary 

 threads. Lines of growth are prominent, particularly on the 

 later whorls; they incline to the right (shell held upright) 

 at an angle of about 45 from the suture halfway to the 

 carina ; thence they curve broadly downward, crossing the 

 carina at right angles and continuing, with a slight turn 

 to the left, into the suture. They are slightly sinuate in the 

 spaces between the secondary and primary threads. Apical 

 angle moderate. Whorls estimated 17 or more in number for 

 complete specimen. Base of body whorl, set off from the 

 lateral surface by the post-sutural secondary thread, sculp- 

 tured by numerous threads of about the third order of 

 strength : of these, two equally spaced, are sometimes more 

 prominent. Length, 130 mm. ; maximum diameter, 24 mm. 



The characters which separate the variety trullissatia from 

 nelsoni are brought out in the discussion of the general 

 group. It is easily recognizable through its generally rugged, 

 angular appearance, and although its relationship to nelsoni 

 is easy to see there is no difficulty in separating the two. It 

 is somewhat similar to T. mimetes Brown and Pilsbry, 70 from 

 Gatun, with the difference that the precarinal surface of 

 trullissatia is much larger, and the carina hence much more 

 protuberant than that of mimetes. The two are not really 

 very close. 



Upper Zorritos. Quebrada de las Alturas. 



Turrit ella infracarinata Grzybowski 

 PLATE III Figs. 9, 10. 



Turritclla infracarinata Grzybowski, Neues Jahrb. f. Min., etc., 

 Beil. Bd. 12, p. 643, pi. 20, fig. 5, 1899. 



"Umgange dachformig abfallend, in }/ 4 der Hohe gekielt, 



Froc. Ac. Nat. Sc. Phila., vol. 63, p. 357, pi- 27, fig. i, 1911. 



