ORTMANN ! TERTIARY INVERTEBRATES. 
139 
65. Venus volckmanni Philippi. 
PI. XXVIII, Fig. 3“’ 6 . 
1887 V. v. Philippi, Tert. & Quart. Verst. Chiles, p. 121, pi. 14, f. 9. 
1897 V. v. var. argentina v. Ihering, in : Rev. Mus. Paul., v. 2, p. 252, 
P'- 7 . f- 45 - 
1899 V. v. v. Ihering, in: N. Jahrb. Miner., etc., v. 2, p. 20. 
Shell suborbicular, very convex ; posterior dorsal margin slightly con- 
vex, forming an obtuse angle with the posterior margin, which forms, with 
the ventral margin, part of an almost regular circle. Apex between f 
and of the length. Area indistinct, nymphae immersed. Lunula cor- 
date, elevated in the middle. Surface with rather widely distant, elevated 
lines, and distinct radiating striae. 
Measurements : Length, ca. 73 mm; height, 70 mm; diameter, 27 (x 2). 
Another individual: length, 55 mm; height, 51 mm; diameter (double), 
35 mm. In the latter, the apex is 15 mm from the anterior end. 
Remarks: Philippi gives the position of the apex as ~ = ca. f of the 
length, v. Ihering as £ = ca. . This difference is apparently in part due 
to the different position given to the shell, as the regular outline of the 
shell renders it difficult to give a uniform position to different specimens. 
The form from Santa Cruz is hardly distinguishable as a variety from 
that from Chili (in 1899 v. Ihering mentions typical individuals from Santa 
Cruz). The convexity of the dorsal margin is variable, and the anterior 
end (below the lunula) is more or less produced in different individuals : 
There are specimens from Santa Cruz completely agreeing with Philippi’s 
figure in this respect. 
The cast from Shell Gap does not show any surface markings, but agrees 
in form. The casts from Lake Pueyrredon, however, show distinct remains 
of the cancellations. The cast from the mouth of Santa Cruz River shows 
the impression of the cardinal teeth : they are those of a true Venus. 
Record of specimens : Mouth of Santa Cruz River, 1 double cast (near 
high water mark), 1 double valve, 2 isolated valves (250' above high tide). 
Shell Gap, Rio Chico, upper horizon ; 1 cast. Lake Pueyrredon, base of 
Tertiary; 3 casts. Lake Pueyrredon, 600' above base; 2 casts. 
Distribution: Patagonian beds of Santa Cruz (v. Ih.) ; Navidad beds 
of Chili : Navidad, Tubul, Millanejo and Lebu (Phil.). 
