OF THE UNITED STATES. 83 
CONCLUSION. 
Ir is well known that there is at present a remarkable 
generic accordance, between the testaceous mollusca of the 
eastern and western shores of the Atlantic ocean; and by 
a reference to No. 2 of the Appendix, it will be seen 
that at least twenty-four species of shells have already been 
identified as common to both. Is it not probable that this 
accordance was formerly as great as at present? It will 
be hereafter seen that I have also traced some identities 
in the tertiary deposits of Europe and America; and 
when we arrive at the Cretaceous group, the highest of 
the secondary series, we find the PECTEN guinquecosta- 
tus, (which has been aptly called the ‘finger post” of 
the chalk formation,) as frequent as it is unequivocal, on 
both sides of the Atlantic. Although I have been un- 
able to satisfy myself of any other zdenizties in the widely 
separated portions of this series, yet the analogues are 
surprisingly obvious, and may be judged of by a mere 
glance at the accompanying plates. 
Again, the analogy is not confined to the Testacea, but 
is observed in the great family of the Saurian reptiles ; for 
there is no perceptible difference between the teeth of 
the Mosasaurus of Europe and that of New Jersey. From 
these and other data scattered through this work, I arrive 
at the conclusion, that when the chalk fossils were living 
inhabitants of the seas of Europe, the organic relics of 
this synopsis were alive in the ocean of America; in 
