8 4 
PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 
(1864, p. 47, pi. 15, f. 12). But here the posterior end is blunt, and the 
sculpture consists only of concentric ribs, and above the posterior ridge 
there are no ribs. 
I cannot find any other species that might be compared with this one ; 
there are numerous species in Tertiary deposits which resemble this one 
in external shape, but the character of the sculpture is here very peculiar, 
especially the coexistence of concentric and radial sculpture, and the 
presence of a larger number of concentric ribs on the escutcheon. 
25. Leda errazurizi (Philippi). 
PI. XXVI, Fig. 3"T 
1887 Nucula err., Philippi, Tert. Quart. Verst. Chiles, p. 196, pi. 41, f. 11. 
1900 Leda err. Ortmann, in: Amer. Journ. Sci., v. 10, p. 378. 
Shell elongate-ovate, apex situated almost in the middle of the dorsal 
margin. Anterior end rounded, posterior acute, but hardly produced 
(about as long as anterior). Posterior dorsal margin straight. Ventral 
margin arcuate. A ridge runs from the apex to the posterior end ; just 
below this ridge is a broad and sharply defined depression. Surface of 
shell with fine concentric ribs, the ribs terminating, near the apex, ab- 
ruptly on the ridge, leaving the escutheon smooth (except for growth- 
lines ; toward the ventral margin, the concentric ribs disappear when 
reaching the depression below the ridge, so that this depression is crossed 
only by fine growth-lines. Anterior hinge teeth ca. 21, posterior ca. 16. 
Length, 13 mm; height, 7 mm. 
Remarks: The specimen from Santa Cruz is the largest, and shows all 
the characters given above. Specimens from Lake Pueyrredon are 
smaller, and are mostly casts, with only fragments of the shell remaining. 
One individual however, shows distinctly the characters of the sculpture : 
the disappearance of the concentric ribs on the depression below the 
escutcheon, and therefore there is no doubt that they belong to this 
species. The outer cast from Arroyo Gio shows distinctly the sculpture 
of this species. The cast from Sierra Oveja is doubtful, as it does not 
exhibit any surface characters ; but the outline agrees well with this 
species. 
In Philippi’s description of this species the surface sculpture is described 
as “ concentrice et tenuiter striata; striis ante marginem dorsalem abrupte 
