I4O PATAGONIAN EXPEDITIONS '. PAL/EONTOLOGY. 



Affinities: In sculpture, this species is closely related to the two fore- 

 going. It is represented in the recent seas of Chili and Patagonia by V. 

 antiqua Kg. (see: v. Ihering, 1897, p. 253). 



66. VENUS DARWINI Philippi. 



PL XXVIII, Fig. 4. 



1887 V. d. Philippi, Tert. & Quart. Verst. Chiles, p. 122, pi. 17, f. 2. 

 1899 V. d. v. Ihering, in: N. Jahrb. Miner., etc., v. 2, p. 19. 



Shell ovato-orbicular, subquadrate, convex. Posterior dorsal margin 

 convex, forming an indistinct angle with the posterior margin. Anterior 

 extremity distinctly narrower than posterior. Apex at about one-fifth of 

 the length. Area indistinct, nymphae immersed. Lunula lanceolate, 

 depressed in the middle. Surface with regular, rather widely distant, 

 elevated concentric lines, and very slight indications of radiating stria::. 

 Inner margins crenulate. 



Length, 73 mm; height, 65 mm; diameter, 17 (x 2) mm. Apex at 15 

 mm from anterior end. 



Remarks: Radiating striae are not shown in Philippi's figure, and, 

 indeed, there are hardly any traces of them in our specimens. 



This species corresponds in size to V. volcknianni, but is more elon- 

 gated, and the concentric lines are a little more widely distant in I/, volck- 

 manni. There is also a slight resemblance to V. difficilis (see above), but 

 in the latter the posterior end of the shell is narrower, and the surface 

 ornaments are quite different. 



Record of specimens: Mouth of Santa Cruz River, 2 right, 4 left valves 

 (in matrix). 



Distribution: Patagonian formation of Santa Cruz (Phil., v. Ih.). 



Affinities: Closely allied in form and sculpture is V. burdigalensis 

 Mayer (see: Hoernes, 1870, p. 129, pi. 15, f. i) from the Miocene of 

 Europe, but the latter differs in the more closely set, and more distinctly 

 lamellar concentric lines, and further, in V. burdigalensis, the hinge 

 makes a transition to the genus Meretrix, while V. darwini seems to be 

 a true Venus. Philippi and v. Ihering do not describe the hinge ; in our 

 specimens only part of it is seen, and seems to possess, in the left valve, 

 only three teeth : at any rate, I do not see any trace of a fourth (lunular) 

 tooth ; this part of the hinge, however, is incompletely exposed. 



