i6o 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
Affinities : As has been pointed out above, the New Zealandian and 
Australian species D. mantelli is closely allied to this species. It is 
found in New Zealand, in the Pareora system of Miocene, according to 
Hutton. 
A closely allied species seems to be : D. gabbi Pilsbry and Sharp (1897, 
p. 470, pi. 10, f. 6, 7, 13, pi. 11, f. 1, 2), from the Oligocene or Miocene 
beds of San Domingo, but it is smaller, and the number of ribs near the 
apex is less. 
Of the European species, D. kickxi Nyst(see: Speyer, 1870, p. 199, 
pi. 21, f. 8— 11) from the Middle and Upper Oligocene seems to be the 
most closely allied species. 
89. Dentalium octocostellatum Pilsbry and Sharp. 
PI. XXXI, Fig. 2. 
1897 D. octocostatnm v. Ihering, in: Rev. Mus. Paul., v. 2, p. 266, pi. 4, 
f. 16 (non D. octocostatum Fraas, 1867). 
1898 D. octocostellatum Pilsbry and Sharp, Man. Conch., v. 17, p. 21 1. 
Shell small, slightly curved, with 6 to 8 longitudinal ribs, which are 
distant, with flat intervals, rendering the cross section polygonal. 
Diameter up to 3.5 mm. 
Remarks: This species differs from the foregoing: (1) in the small 
size; (2) in the smaller number of ribs; v. Ihering gives 8-9, but his 
figure shows — as far as can be made out — an individual that had certainly 
not more than six ribs. In our specimens, one (the largest) has only 6 
distinct ribs, with two very indistinct ones (on the lateral intervals). The 
other individuals have 7 or 8. D. sulcosum , at the same size, has always 
at least 9 or 10 ribs. 
(3) The taper in both species is different. Our largest individual of 
the present species is 25 mm. long, the diameter at one end is 2.3 mm, at 
the other 3.5 mm. An individual of D. sulcosum, 24 mm long, increases 
from 2.3 to a little over 4 mm. 
The specimens from Arroyo Gio are casts, but they agree in size, curv- 
ature and taper with this species. 
Records of specimens : Mt. of Observation, upper horizon, 6 fragments; 
Arroyo Gio, 2 casts. 
Distribution: Jegua quemada, Suprapatagonian beds (v. Ih.). 
