114 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



Brachiopods, which are characteristic for the lower part of the Lake 

 Pueyrredon (Rio Tarde) 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. PECTINID^. Lamck. 



Gen. PECTEN Mueller. 

 37. PECTEN PROXIMUS v. Ihering. 



PI. XXI, and PI. XXII, Fig. i-. 



1897 P- centralist. 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 i 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 



