226 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



narrow, canal very short, represented only by a rounded sinus. Colu- 

 mella with 4 subequal folds. Outer lip thickened, smooth within. 



Height, 1 1 mm ; diameter, 5 mm ; length of mouth, 6.5 mm. 



Remarks: This species differs from the other Patagonian species in the 

 perfectly smooth surface and very elongated form. 



Record of specimens : Mouth of Santa Cruz River, 5 sp. 



Affinities: The Pliocene and recent M. styria Dall (1890, p. 54, pi. 5, 

 f. i) resembles this species in form, but it is smaller, still more slender, 

 and the spire is longer. 



Gen. VOLUTA L. 

 156. VOLUTA TRIPLICATA Sowerby. 



PI. XXXV, Fig. 4. 



1846 V. t. Sowerby, in: Darwin, Geol. Observ. S. America, p. 262, pi. 4, 



f. 74. 



1887 V. t. Philippi, Tert. & Quart. Verst. Chiles, p. 70, pi. 7, f. 8-12. 

 1897 V- dorbignyana v. Ihering, in: Rev. Mus. Paul., v. 2, p. 303 (teste 



v. Ihering). 

 1899 V. triplicata v. Ihering, in: N. Jahrb. Miner., etc., v. 2, p. 33. 



Shell moderately elongated, subfusiform. Whorls 6, surface with 

 numerous, distinct, and rather crowded spiral cords, and a number of 

 longitudinal ribs (8-16), which are rather prominent; their upper end 

 terminates abruptly some distance from the suture, being often tuberculi- 

 form ; the uppermost part of the whorls, near the suture, is more or less 

 distinctly concave. Last whorl moderately inflated, mouth (including 

 canal) about half as long as the whole shell. Columella mostly with 3 

 plaits, which are sometimes subequal, and sometimes the uppermost is 

 weaker than the others and may disappear; in one case there are 4 dis- 

 tinct plaits, the uppermost the smallest. 



Measurements: Height, 106 mm; diameter, 46 mm (large part of canal 

 gone). Height, 92 mm ; diameter, 41 mm (large part of upper end gone). 

 Height, 87 mm ; diameter, 34 mm (almost complete, only apex wanting). 

 Height, 44 mm; diameter 21 mm (complete, young). 



Remarks: The most important characters of this species have already 

 been pointed out by v. Ihering, and are found in the relation of the length 



