mn: bis se 
and we trust that this effort will be followed up in ; 
Europe, until all the species shall be presented in — 
good models.” 
It is with much hesitation that I have proposed new 
names for so many of these animal remains ‘¢ of other 
times ;”? fearing lest the only result of my labor 
would be to swell some future list of synonyms. 
Much difficulty arises from the very nature of the in- 
vestigation. The peculiar characters of the fossil are — 
often so obliterated, or so entirely obscured by the 
rock in which it is embedded, as to occasion a doubt, 
which a perfect specimen would instantly remove : 
while the appearance of the animal in its young, and 
in its adult or mature state, are so altogether un- 
known to us, that we are perpetually liable to fall into 
error, in our attempts at discrimination. After pub- 
lishing the Monograph, I had a hope that more expert, 
experienced and diligent naturalists would have en- 
tered this extensive, fruitful and almost untrodden 
field of investigation, and that their researches would 
have established or destroyed the species which I had 
suggested ; but in this anticipation I have been dis- 
appointed. I shall therefore continue to describe 
with caution, these interesting relics, as they are sent 
to me by the liberality of my friends, or as they fall 
under my observation during other researches into 
the natural history of our prolific country. Thus far 
[have had no reason to alter any of the opinions 
which have been heretofore advanced, though I am — 
