1 92 PATAGONIAN EXPEDITIONS-: PALAEONTOLOGY. 



Fam. TURRITELLID^E Gray. 



Gen. TURRITELLA Lmck. 

 123. TURRITELLA EXIGUA Ortmann. 



PI. XXXI, Fig. 12"' \ 



1899 T. e. Ortmann, in: Amer. Journ. Sci., v. 8, p. 430. 



Shell small, with 10 whorls, about 4 times as high as broad at the base. 

 Suture deep, whorls convex, with 5 to 7 spiral ribs, which are rather 

 crowded, and often alternately stronger and weaker. The stronger ribs 

 sometimes appear to be slightly granulated. 



Height, 15 mm; diameter, about 4 mm. 



Remarks: In the small size of the shell this species differs from all other 

 Patagonian Turritellce, and agrees with the two dwarf forms described by 

 Philippi from the Navidad beds of Chili : T. trilirata and parvula. But 

 the latter can easily be distinguished by their flat whorls and smaller 

 number of ribs. 



Record of specimens : Punta Arenas, horizon II (lower Magellanian), 

 over 100 sp. 



Affinities: As regards the sculpture and the convex whorls, this species 

 finds many analogous forms in Eocene, Miocene and Pliocene beds, as 

 the type of which we may take the Oligocene and Miocene T. turris Bast, 

 of Europe. But taking into consideration the small size of the present 

 form, we find that the species younger than Eocene are very much larger, 

 and only in Eocene beds do we find a few that might be compared with 

 our species in this respect also. One of the most closely allied forms 

 seems to be : T. granulosa Deshayes, from the Eocene of France, but this 

 one is still considerably larger than T. exigua and the whorls increase 

 more rapidly. 



124. TURRITELLA AMBULACRUM Sowerby. 



PI. XXXI, Fig. i3> 6 . 



1846 T. ambulacrum Sowerby, in: Darwin, Geol. Observ. S. Amer., p. 



257, pi. 3, f. 49. 

 1846 T. suturalis Sowerby, ibid., p. 257, pi. 3, f. 50. 



