136 PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 



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, y 2 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, i left valves, and several fragments. 



Affinities: I have compared, in my preliminary report, this species with 

 V. subsulcata 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"'". 

 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 y$ of the length. 

 Area indistinct, shorter than the posterior part of the dorsal margin. Nym- 

 phae X~K as l n g as ^e 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- IJ 6> 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. 



