ORTMANN : TERTIARY INVERTEBRATES. 183 



form a complete revolution, it completes, in G. mamillaris, the circle at 

 least once (in small individuals), and 'i ^ to 2 times in larger individuals. 



Record of specimens : Cape Fairweather, 3 1 casts. 



Distribution : This species is found living on the western coast of South 

 America, from Chili to California (see Tryon, 1. c., p. 120). 



Gen. SIGAPATELLA Less. 

 114. SIGAPATELLA AMERICANA Ortmann. 



PI. XXXII, Fig. 9"'*. 



1900 S. a. Ortmann, in: Amer. Journ. Sci., v. 10, p. 373. 



Shell subcircular or subelliptical, depressed. Apex distinctly excentric. 

 Surface with irregular, concentric, slightly lamellate striae, crossed by very 

 fine radial rugosities. Internal diaphragm spiral, columella excentric, 

 margin of diaphragm slightly concave and slightly reflected at the columella. 



Measurements of a specimen from Punta Arenas : Height, 3 mm, diam- 

 eter, 17 mm; of a specimen from Santa Cruz: Height, 16 mm, diameter, 

 49 mm ; of another from Santa Cruz : Height, 5 mm, diameter, 27 mm. 



Remarks: As to the generic name Sigapatella see Tryon, 1886, p. 104. 



The radial plications or rugosities are very fine and sometimes indis- 

 tinct. In our smaller individual from Santa Cruz, which is a little worn, 

 there are no traces of them left. 



Record of specimens : Mouth of Santa Cruz River, 2 sp. ; Punta Arenas, 

 above horizon V (Patagonian), 4 sp., found inside of Ostrea ingens. 



Affinities: Trochita colchaguensis Philippi (1887, p. 93, pi. 1 1, f. 5) from 

 La Cueva, Colchagua, Chili (age doubtful), may be identical, as well as 

 the recent species S. calyptrcsiformis Lmck. (= tomentosa and mac^llata, 

 Qu. & Gaim.), from Australia and New Zealand (see Tryon, 1886, p. 122, 

 pi. 35, f. 96-99): but these forms do not show the sculpture of our species. 



A species has been mentioned under the name of Trochita dilatata Sow. 

 = maculata Qu. & Gaim., by Zittel (1864, p. 43, pi. 15, f. 8), from the 

 New Zealand Miocene, but it seems doubtful whether this is a Sigapatella 

 at all. Calyptrcea maculata Qu. & Gaim., is given by Hutton (1873, p. 13) 

 from the Oamaru, Pareora, and Wanganui beds of New Zealand, and thus 

 it would pass from the Oligocene upward to Recent times. 



No other fossil Sigapatella being known, our species would point most 

 distinctly to Neogene age. 



