1 36 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
the whole of the posterior dorsal margin of the shell. Lunula oval, flat. 
Surface with close and regular concentric furrows, and with some concen- 
tric lines of growth, the latter more crowded near the lower margin and 
irregular. Concentric furrows sharp, not interrupted, to i mm distant 
from each other. Margin of shell not crenulated within. 
Length, 75 mm; height, 64 mm; diameter, 18 ( x 2) mm; apex at 16 
mm from anterior end. 
Remarks: Surface more or less well preserved in specimens from the 
lower horizon, but in those from the upper horizon obscured by adhering 
coarse matrix, although still recognizable. 
Record of specimens : Punta Arenas, horizon II (lower Magellanian) ; 
2 double, 2 left valves. Punta Arenas, horizon III (upper Magellanian) ; 
2 right, 1 left valves, and several fragments. 
Affinities : I have compared, in my preliminary report, this species with 
V. sub sulcata Phil. (1887, p. 115, pi. 17, f. 7) from the Cretaceous beds of 
Chile. And indeed, this seems to be the most closely allied form. 
62. Venus arenosa Ortmann. 
PI. XXVIII, Fig. 2“A 
1899 V. a . Ortmann, in: Amer. Journ. Sci., v. 8, p. 428. 
Shell transversely elliptical, moderately swollen. Posterior end hardly 
narrower than the anterior. Apex situated at about f of the length. 
Area indistinct, shorter than the posterior part of the dorsal margin. Nyrii- 
phae as long as the area. Lunula indistinct. Exterior surface 
with strong concentric lines of growth, which have between them finer 
concentric striae. Hinge that of a true Venus . 
Length, 60 mm; height, 44 mm; diameter, 15 (x 2) mm. 
Remarks: The surface markings are obliterated on account of the 
closely adhering matrix. 
Record of specimens : Punta Arenas, horizon III (upper Magellanian), 
3 right valves. 
Affinities: This species possesses a very characteristic, elongated out- 
line, and resembles in this character — as I have pointed out in my pre- 
liminary report — V. landbecki Phil. (1887, p. 116, pi. 20, f. 8) from the 
Cretaceous of Chili. V. landbecki , however, differs in the position of the 
apex, more inflated valves, and more distinct area. 
