ORTMANN : TERTIARY INVERTEBRATES. 141 



67. VENUS NAVIDADIS Philippi. 



PI. xxvn, Fig. i2:. 



1887 V. nav. Philippi, Tert. & Quart. Verst. Chiles, p. 126, pi. 14, f. 4. 

 1897 V. striatolatnellata v. Ihering, in: Rev. Mus. Paul., v. 2, p. 253, pi. 



7. f- 44- 

 1900 V. nav. Ortmann, in: Amer. Journ. Sci., v. 10, p. 380. 



Shell ovate, slightly convex, anterior and posterior ends rounded. 

 Apex at about l / of the length. Area indistinct, nymphae immersed. 

 Lunula lanceolate, concave. Surface with concentric lamellae, between 

 the lamellae fine concentric striae. Margin on inner side not crenulate. 



Length, 63, 39 mm; height, 50, 31 mm; % diameter, 10, 7 mm. 



Remarks: As v. Ihering has already mentioned, the external form is a 

 little variable. His type specimen measures: L. 79, H. 68 (ratio H. : 

 L. = i : 1.16), while another one is only 64 high by 79 long (ratio = i : 

 1.23). Philippi gives: L. 47, H. 38 (ratio = i : 1.23). The ratio of our 

 specimens given above is = i : 1.25, and i : 1.26; they are, accordingly, a 

 little more elongated than even v. Iliering's second individual, while that 

 figured by v. Ihering appears exceptionally high. In all other respects 

 our specimens agree well with v. Ihering's description of V. striato-lamcl- 

 lata, and I cannot discover any difference between this species and V. 

 navidadis. V. Ihering believes them to be closely allied, but points to 

 a difference in the lunula, which he takes from the figure of V. navidadis. 

 In the discription of both forms, however, Philippi and v. Ihering use the 

 identical words: "lunula profundata," so that it is impossible for me to 

 see the difference. 



In the description Philippi gives the position of the apex at *4 of the 

 length ; but his figure shows it distinctly at l / . 



The casts from Upper Rio Chalia possess the outline of this species, but 

 no traces of the shell are preserved. 



Record of specimens : Mouth of Santa Cruz River ; 2 left, 5 right valves. 

 Upper Rio Chalia, 4 casts. 



Distribution: Suprapatagonian beds of Jegua quemada (v. Ih.) ; Navi- 

 dad (Phil.). 



Affinities : This species comes near V. arenosa described above, but K 

 arenosa is still more elongated (ratio = i : 1.36 to i : 1.5), and further, the 



