ORTMANN : TERTIARY INVERTEBRATES. -105 



every single one of the figures of the different supposed species. And, 

 in addition, we possess numerous intermediate forms, and individuals 

 combining characters of these so-called species. 



3. This large species of oyster continues its existence all through the 

 (Miocene) Patagonian formation, as well as upward into the Pliocene 

 Coquimbo beds of Chili. 



Now, the same is true in Patagonia. The identical form reappears in 

 the Cape Fairweather beds, which are separated from the Patagonian beds 

 by the whole of the Santa Cruz formation. (At the cafion near Sierra 

 Oveja, No. 11, O. ingens has been found in beds interstratified with the 

 lower Santa Cruz beds.) I cannot find any specific difference between 

 the Patagonian and the Cape Fairweather forms, although there are some 

 slight and almost insensible differences in the general features : the Cape 

 Fairweather form does not grow quite as large, the shell although still 

 very thick is not quite so gigantic in mass, the outline is more distinctly 

 and more frequently of a triangular shape ; the crenulations of the margin 

 of the upper valve near the hinge occur more frequently, but still there 

 are many specimens which show no traces of them. 



An oyster closely resembling in these characters the Cape Fairweather 

 form is found in the uppermost oyster bed at Punta Arenas (No. 22), 

 and in the uppermost beds at Lake Pueyrredon (No. 19). 



As to the identification of the Patagonian oyster with the New Zea- 

 landian form, I would make the following remarks : 



O. ingens and nelsoniana of Zittel are apparently identical. The latter 

 is smaller, and accordingly younger, but Zittel mentions the character of 

 the extraordinary thickness of the shell. O. ingens is a large individual, 

 of elongated shape, and with a very long and broad area. Zittel says, 

 that the area is limited on each side by a groove (sulcus), a character that 

 is seen in some of our specimens. I do not find a single character by 

 which it is possible to distinguish our species from the New Zealand- 

 form, and, indeed, I can pick out individuals agreeing closely with the 

 figures given by Zittel of O. ingens as well as of O. nelsoniana. 



A very closely allied, if not identical, form is O. stiirtiana Tate (1886, 

 p. 97, pi. 6, f. i), from the Miocene River Murray Cliffs, Australia. 



Ostrea rostrata of Hupe (see Philippi, 1887, p. 213), from Coquimbo, 

 of which no figure is known, seems to agree, according to the descrip- 

 tions, with the form called by Moericke O. beneckei. If that should prove 



