ORTMANN ! 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. philippii does not differ at all in this respect from O. 
hate hap 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 
i8 99 (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. E), while, on the other hand, the 
