23 
lations being all visible and somewhat diffi¬ 
cult, in some species, to distinguish from those 
of the abdomen. These articulations, which 
are generally ten in number, are composed of 
a variety of immovable plates as in the other 
genera. The inferior surface of the caudal 
end of the trilobite had never been observed 
by any naturalist, till my friend Dr. Cohen 
obtained some fragments of the genus caly- 
mene from the neighbourhood of Berkley 
Springs, in Virginia, in some of which that 
structure was developed. These were kindly 
sent to me for examination, along with those 
of the buckler just described. 
From our researches we have ascertained, 
that the inflexible margin which surrounds 
the caudal end or tail of the calymene bufo, 
is not reflected beneath the body of the animal, 
as might be expected, but that there is joined 
to it by a suture a slightly concave horizon¬ 
tal surface. This surface is lunate, being 
broader below the articulations of the verte¬ 
bral column, and gradually diminishing on each 
side towards the horns of the crescent, which 
