ORTMANN I TERTIARY INVERTEBRATES. 103 



specimens). As to the situation of the muscular scar (character 4), it may 

 be remarked, that the more central position is found in more rounded 

 individuals, and is without doubt directly dependent on the outline of 

 the shell. 



As to the third character introduced by v. Ihering, taken from the liga- 

 mental groove of the upper valve, I fail to see any constancy in it. Indeed, 

 there is considerable variation, it being sometimes concave, sometimes 

 flat, sometimes slightly convex, and the lower margin is more or less 

 prominent. The convex character, however, of the surface of the groove, 

 is exhibited in comparatively few individuals, and the prominence of the 

 lower margin is not always connected with a convexity of the surface. My 

 type-specimen of O. pliilippii does not differ at all in this respect from O. 

 hatcheri, and my specimens of the true O. patagonica from Entrerios (sent 

 by v.- Ihering to the Princeton Museum) do not show a remarkable con- 

 vexity, and also among my specimens of the true O. patagonica from S. 

 Julian the fossa is sometimes flat and sometimes slightly convex. On the 

 other hand, I have specimens of the typical O. hatcheri with the lower 

 margin of the ligamental fossa very prominent, although its surface is flat, 

 and many individuals from Cape Fairweather (see pi. XVIII) show a dis- 

 tinctly concave fossa. I possess even a few individuals with circular out- 

 line, which have a slightly convex and strongly prominent fossa: on the 

 whole, this latter development is rare among our material, and shows all 

 possible transitions to a concave fossa. Therefore, it is evident, that this 

 character is of no use for distinguishing O. hatcheri and philippii, and 

 also cannot be used for the distinction of the Patagonian oyster from O. 

 patagonica. 



The form with the crowded lamellae from the Patagonian beds (v. Iher- 

 ing following Ameghino, alleges that it is restricted to the so-called Supra- 

 patagonian beds), has also been confounded by v. Ihering with the true 

 O. patagonica, although he confirms the presence of the characteristic cren- 

 ulations of the upper valve in specimens from Parana (Entrerios). In 

 1899 (p. 10), he emphasizes this character, but he says that crenulations 

 are not always missing in the oyster of the Patagonian beds and not 

 always present in the Entrerios oyster. But according to my expe- 

 rience the first is the case in a very limited degree : the crenulations in 

 Patagonian shells if present at all are found only for a very short dis- 

 tance near the area (see pi. XVIII, fig. i 6 ), while, on the other hand, the 



