ORTMANN : TERTIARY INVERTEBRATES. 157 



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 1 6 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. DENTALIID^E. Gray. 

 Gen. DENTALIUM L. 



88. DENTALUM SULCOSUM Sowerby. 



PI. XXXI, Fig. !. 



1846 D. sulc. 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. sulc. Philippi, Tert. & Quart. Verst. Chiles, p. 106 (partim). 

 1887 D. maj. Philippi, ibid., p. 106, pi. 12, f. n. 

 1887 D. gayi Philippi, ibid., p. 107, pi. 12, f. 19 (juv.). 

 1889 D. patagonicum Rochebrune & Mabille, in: Miss. Sci. Cape Horn, 



v. 6, p. 98. 



