782 The American Naturalist. [September, 
three rows of crescentic tubercles belong to the upper series, as 
I have described them.” 
In reply, I may say that undoubtedly some cfescentic tuber- 
cular teeth, in three rows, will be found in the upper jaws of some 
Cretaceous species, if for no other reason, because the ancestors 
of Polymastodon will be found in the Cretaceous, and these 
ancestors will exhibit three rows of subcrescentic tubercles in the 
upper molars, since such is the character of the large Polymas- 
todon upper molars. 
It remains for the author to show specifically that the types of 
Selenacodon and Tripriodon are maxillary teeth. I should 
myself have considered them as such but for the fact that the 
type of Dipriodon robustus, with two rows of tubercles, was de- 
scribed as a maxillary tooth, and figured with a supposed frag- 
ment of the zygomatic arch attached to the alveolar border. If 
this tooth proves to be mandibular,.and the molars with three 
rows of crescents are shown to be maxillary, the author will have 
substantiated his second statement ; but such proof will not help 
him out of his synonomic dilemma, for it will still appear that he 
has founded three families, five genera, and as many species upon 
different teeth belonging to the same dental series, and all syn-- 
onyms of Meniscoéssus. 
Enough has been said to make it clear that, whatever evidence 
the author may hold in reserve for his future memoir, this “ Note 
on Mesozoic Mammalia” contains no positive evidence in defence 
of his “ Cretaceous Mammalia.” ; 
In closing, I may quote a concluding paragraph in the author’s 
reply: “Noone who has earnest work to do can afford to spend 
time in the ungracious task of pointing out errors in the work of 
others.” I have always been of the same opinion that criticism is 
an ungracious and thankless task. In this case I deferred my 
“Review” for nearly two years, and endeavored to avoid it 
entirely by sending to the author all my main points of doubt in 
regard to his paper, and asking him to revise it. After waiting 
for the author to avail himself of this opportunity, I came to the 
conclusion that the “ Cretaceous Mammals,” sent out with the 
authority of the distinguished author’s name, and under the 

Seen i Fie ain ne ae ete Sree a toa Cor ne Ee a A 





