ORTMANN : TERTIARY INVERTEBRATES. 
109 
15. East end of Lake Pueyrredon; 1 lower valve. 
Young, oval. 
16. Lake Pueyrredon, base of Tertiary; 1 lower valve. 
Form of 0 . hatcheri , but lamellae in posterior half more crowded. 
A fragment found washed out just below these beds, in the same 
matrix and of the same color, indicates a more elongated shell, with long 
area and crowded lamellae. 
1 7. Lake Pueyrredon, 6oo' above base ; 2 double valves. 
The smaller one is a typical O. hatcheri ; the larger one is more ovate, 
with crowded lamellae. 
18. Lake Pueyrredon, extreme top of Patagonian beds; 2 double 
valves. 
Both broadly oval, like O. hatcheri , and with broad area, but lamellae 
more crowded. 
19. Lake Pueyrredon, marine beds overlying Santa-Cruz beds ; 8 
double valves. 
No characters of O. hatcheri ; outline irregularly oval or triangular. 
Area triangular, shorter or longer. ' Size medium or small. Ribs indis- 
tinct or none. Crenulations in smaller valve in 3 specimens. Ap- 
proaches distinctly the Cape Fairweather form. 
20. Punta Arenas, horizon V, lower layer (“below V”) ; 2 double, 3 
upper valves. 
Both double valves are the typical O. philippii : long-ovate, area very 
long, in one of them incurved ; lamellae in the latter quite distant. 2 of 
the upper valves agree with this form, but the third is subcircular, with a 
broad area, and distant lamellae, except near the margin, and it would 
thus correspond to O. hatcheri. 
21. Punta Arenas, horizon V proper ; 1 double, 8 lower, 2 upper valves, 
Lower valves all much elongated, long-oval, beak much produced, nar- 
rowed toward the tip, area very long (see pi. XIX, fig. P) ; correspond- 
ing to O. philippii. Lamellae not very distant, crowded near the margins. 
One upper valve is oval, with distinct crenulations near the area. The 
area of these specimens corresponds to Philippi’s figure of the area of 
O. bourgeoisi. 
22. Punta Arenas, “above horizon V”; 2 double, 2 lower valves. 
Outline ovate or subtriangular. Area triangular, not very long. In 
one of the isolated lower valves the lamellae are very distant, as in O. 
