ORTMANN I TERTIARY INVERTEBRATES. 1 57 
margin, but cuts off a small, crescentric piece, which seems to represent 
the impression of the callus. 
The ribs (on the cast) are simple, but near the anterior end of the shell 
they are crossed by three to four radiating lines, forming small nodes at 
the points of intersection. Anterior end of shell not rectangular, but 
rounded. 
Length, 9 mm ; height, 4 mm ; diameter (double), 4 mm. Largest 
individual : height, 7 mm, but incomplete in length, which was probably 
about 16 or 18 mm. 
Remarks: I was first inclined to regard this form as the young stage 
of M. patagonica. But we possess a single, fragmentary valve, coming 
from the same piece of rock with the rest, which is a little larger (see 
measurements above), and corresponds in size to our smallest individuals 
of M patagonica. Yet this specimen shows the narrow radiating 
groove, the obtuse angle between the lines of growth and the concentric 
ribs, and the simple character of the latter, while the young specimens of 
M. patagonica (from Mt. of Observation) agree in these respects with 
larger individuals of that species. 
Record of specimens : Mouth of Santa Cruz River, ca. 100 specimens. 
SCAPHOPODA. 
Fam. DEN TALIIDAi Gray. 
Gen. DENTALIUM L. 
88. Dentalum sulcosum Sowerby. \ 
PI. XXXI, Fig. i“A 
1846 D. side. Sowerby, in: Darwin, Geol. Observ. S. Amer., p. 263, 
pi. 2, f. 2. 
1846 D. majus Sowerby, ibid., p. 263, pi. 2, f. 3. 
1887 D. side. Philippi, Tert. & Quart. Verst. Chiles, p. 106 (partim). 
1887 D. maj. Philippi, ibid., p. 106, pi. 12, f. 11. 
i88 7 D.gayiPh ilippi, ibid., p. 107, pi. 12, f. 19 (juv.). 
1889 D. patagoniemn Rochebrune & Mabille, in: Miss. Sci. Cape Horn, 
v. 6, p. 98. 
