
OM The American Naturalist. [July, 
the Allotheria. I have probably seen all the Mesozoic mammals 
examined by Prof. Osborn in Europe, and likewise quite a num- 
ber of others, including the type of Stereognathus. He is cer- 
tainly wrong in several of his main conclusions, and in others 
there are many facts against him. 
A more correct restatement of some of the characters of this 
group would be as follows: 
1. No true Plagiaulacide are known with three rows of tuber- 
cles on the upper molars. 
2. No Allotheria are known with certainty to have three rows 
of tubercles on the lower molars. 
A careful study, moreover, of the known specimens of the true 
Plagiaulacide would have shown him the strong probability, at 
least, that the genus Bolodon, which he makes the type of a dis- 
tinct family, is based on the upper jaws of Plagiaulax; also, the 
probability, as I have before suggested, that the type of Stereog- 
nathus, of which he makes another of his numerous families, is 
an upper jaw, although described as a lower one. 
Bearing in mind these points, Prof. Osborn’s main criticisms 
are seen to be without foundation, and the errors largely his own. 
By substituting theory for the actual study of well-preserved 
specimens, he has unwittingly placed on record the fact that he 
cannot tell upper from lower teeth in Mesozoic mammals, nor the 
teeth of reptiles and fishes from those of mammals. 
There is now conclusive evidence that the Cretaceous molar 
teeth with three-rows of crescents belong to the upper series, as 
I described them. Prof. Osborn’s reference of these to the lower 
jaw is based merely on theory, with only conjecture to support it. 
The same fundamental error runs through most of his reviews, 
and measures the value of his criticism. i 
Another unfortunate error of Prof. Osborn was mistaking the 
tooth of a reptile for the premolar of a mammal, and not only 
describing and figuring it as such, but making this a basis for 
using a generic name (Meniscoëssus), against well-known laws of 
nomenclature. This supposed premolar he figures and describes 
in his Mesozoic Mammalia (p. 218), and has elsewhere strongly 
defended its mammalian character. There is not a particle of — 
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