126 PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 



Measurements (of type specimen): Length, 16 mm; height, 14 mm; 

 of specimens from Santa Cruz : Length, 18.5, 15. 5 mm; height, 17, 14.5 

 mm. 



Remarks: This species was first described by the present writer in 1899 

 from a few poorly preserved individuals from the Magellanian beds of 

 Punta Arenas. Later, among the last set of fossils brought home by Mr. 

 Hatcher, I found a larger number of better preserved valves of a small 

 Cardita from the Patagonian beds of Santa Cruz, which agree completely 

 with the Punta Arenas fossil. The chief characters of this species are : 

 the shape and the size of the shell, and the number and shape of the ribs. 

 Young individuals of C. incequalis, of the same size as this species, may 

 be distinguished at a glance by the larger number of ribs. C. volckrnanni, 

 which is closely allied, differs in the smaller number of ribs. 



Record of specimens: Punta Arenas, horizon III (upper Magellanian), 

 3 isolated right valves, 2 valves in matrix ; Mouth of Santa Cruz River, 

 23 right, 17 left valves; Mt. of Observation, upper horizon, i double, 4 

 right, i left valves. 



Affinities: I compared this species with C. elegans Lmck. of the Euro- 

 pean Eocene. But since there are so many similar species known from 

 Tertiary deposits, it is impossible to say that just this one is the most 

 closely allied form. 



This is so far the only species that is common to the Magellanian and 

 Patagonian beds. 



51. CARDITA VOLCKMANNI Philippi. 



PI. XXVI, Fig. 6. 



1887 C. v. Philippi, Tert. and Quart. Verstein. Chiles, p. 173, pi. 37, f. 4. 

 1900 C. v. Ortmann, in: Amer. Journ. Sci., v. 10, p. 378. 



The only difference from the preceding species is the number of the 

 radial ribs: there are only 15 of them. The ornamentation of the ribs is 

 not preserved in our specimens. 



Record of specimens : Lake Pueyrredon, 600' above base of Tertiary, 

 6 casts. 



Distribution: Navidad beds of Tubul, Chili (Phil.). 



