30 
but its calcareous covering to the enemy; or 
they may supply the place of antennse, for 
which their form and contiguity to the mouth 
and brain would seem to render them pecu¬ 
liarly applicable.” The first conjecture above 
noticed was ingenious, and will no doubt be 
confirmed when the lower surface of the tail 
is discovered. The inferior organization of 
the calymene bufo has at any rate given great 
plausibility to this opinion. 
We have also carefully examined another 
fragment representing a similar structure. 
The original fossil was found in Ohio, and 
is now in the possession of W. Wagner, Esq. 
of Philadelphia. The rock on which it occurs 
is a gray limestone full of other petrifactions. 
This lunate structure differs essentially from 
the one noticed by Dr. Dekay; the points of 
the crescent are rounded and do not curve 
towards each other; the terminations are not 
raised and translucent, but the whole surface 
is nearly flat. It, however, formed, undoubt¬ 
edly, a portion of the under surface of some 
triiobite, whether that of an asaphus, an iso- 
