PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
114 
Brachiopods, which are characteristic for the lower part of the Lake 
Pueyrredon (Rio JTarde) section, and belong undoubtedly in the Pata- 
gonian series: thus the Tertiary age of our fossil, and its association with 
Patagonian fossils seems to be well established. 
Fam. PECTINIDPE Lamck. 
Gen. PECTEN Mueller. 
37. Pecten proximus v. Ihering. 
PI. XXI, and PL XXII, Fig. i« 
1897 P- centralis v. Ihering, in: Rev. Mus. Paul., v. 2, p. 229, pi. 8, f. 
48, 49 (non P. centralis Sow.). 
1897 P* proximus v. Ihering, ibid, in tabula. 
1900 P. prox. Ortmann, in: Amer. Journ. Sci., v. 10, p. 379. 
Valves equilateral, unequal, the left one flat, the right one convex. 
Outline suborbicular. Ears large, subequal, the anterior one a little 
larger; byssal sinus wanting. Sculpture of the convex (right) valve: 
about 6 large, rounded principal folds, the 2-4 median ones distinct, the 
lateral ones indistinct. Each fold with 4-8 strong, radial ribs. Intervals 
between the folds concave, a little narrower than the folds, near the apex 
of the shell without ribs, and finely squamulate. Toward the lower 
margin strong ribs begin to develop in the intervals (from 1 to 5), and, 
on the margin, the whole surface of the shell, folds as well as intervals, 
are covered with strong radial ribs. The finely squamulate sculpture is 
found on the ribs also, but toward the margin it disappears through 
obliteration by transverse larger squamae, which develop on the ribs. 
The ribless intervals are different in extent in different individuals : some- 
times they begin to show ribs at an earlier age than in other cases. Flat 
(left) valve of a similar sculpture: 5-7 principal folds, but intervals 
broader than the folds, ribs more strongly squamate, the squamae begin- 
ning nearer to the apex. Ears in both valves with radiating ribs, which 
are less strong than those of the valves, subequal, and squamose. 
Largest valve : Height, 21 cm; width, 22.5 cm (but not quite complete). 
Remarks'. Young individuals, which have the intervals between the 
large folds smooth (except for minute squamulae) exhibit quite a different 
