ORTMANN : TERTIARY INVERTEBRATES. 
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The taper of the young shell is apparently more considerable than in 
the old : a fragment 29 mm long is, on the one end, 3 mm in diameter, 
on the other, 5.5. Another one, 58 mm long, is on one end 7 mm 
in diameter, on the other 10 mm: this latter fragment thus increases 
only 3 mm, where we should expect — at the rate of the first one — about 
5 mm. 
In D. giganteum Sowerby (1846, p. 263, pi. 2, f. 1), and Philippi (1887, 
p. 105, pi. 12, f. 9), from Navidad, the sculpture is different, consisting of 
shallow and narrow grooves, separated by rounded and low intervals. 
According to the figure, D. sulcosum of Philippi (pi. 12, f. 10), 
from Navidad is certainly different from D. sulcosum of Sowerby, and 
it closely resembles D. giganteum , but the furrows are much deeper 
and more distinct. The specimens, however, mentioned by Philippi 
from Santa Cruz as belonging to D. sulcosum, belong no doubt to the 
true D. sulcosum. 
D. lebuense Philippi (1887, p. 106, pi. 12, f. 18), from Lebu and Llan- 
cahue resembles a young D. sulcosum , but it is much straighten 
D. gayi Philippi (Matanzas and Carauma), comes no doubt into the 
synonymy of D. sulcosum : the figure resembles exactly a young individual 
of the Santa Cruz species. 
D. patagonicum of Rochebrune and Mabille, and v. Ihering, is certainly 
identical with our species : we have received from v. Ihering* a fragment 
of medium size under this name, and this agrees completely with our D. 
sulcosum. 
D. mantelli Z ittel (1864, p. 45, pi. 13, f. 7), from New Zealand, Victoria 
and South Australia (Tate, 1887, b, p. 190), and Tasmania (Pritchard, 
1896, p. 126), comes very near to D. sulcosum. The only difference (ac- 
cording to the figure) is the much stronger curvature of the shell. (Tate, 
1887, b, p. 1 91, says : D. giganteum of which solidum Hutton is a synonym 
is distinct though conspecific with D. mantelli, a sentence that is not quite 
clear.) 
Record of specimens : Mouth of Santa Cruz River, 59 fragments ; San 
Julian, Darwin Station, 2 casts ; Lake Pueyrredon, base of Tertiary, 1 
broken and compressed specimen. 
Distribution: Santa Cruz (Phil., Roch. & Mab., v. Ih.), Patagonian 
formation (v. Ih.) ; Navidad beds of Chili: Navidad, Huafo Island (Sow.), 
Ancud, Llancahue, Tubul, Matanzas, Carauma (Phil.). 
