Remarks on the Trilobite. 35 
or under surface of the buckler. By this peculiar mechanism, 
whenever the animal rolled itself into a ball, to give protection 
to the soft parts of the abdomen, the protuberance under the 
shield would be introduced into the cavity below the tail, and 
thus retain the whole shell in a fixed position. In this position, 
with the tail closed upon the buckler, the calymene is often 
found. 
Professor Wahlenberg considers those trilobites only as perfect 
animals, which are found rolled, the others being merely exuded 
or cast-off shells, and in such alone, he remarks, can we expect 
to discover the organization of the inferior surface. Most of the 
fragments from Berkley Springs, which have occasioned my pre- 
sent remarks, are found rolled up or partially coiled animals. All 
trilobites have not, however, this power ; indeed, it seems to be 
principally confined to those only whose extremities are rounded 
and nearly equal in size. The rolled position would afford to the 
paradoxides and to many of the asaphs, but little security against 
the attacks of their enemies, and we rarely if ever find them in 
this attitude. The remark of Professor Wahlenberg above cited, 
though illustrated by the specimens now under consideration, we 
think of far too general a nature. 
The deep cavity beneath the tail in the fragments which we 
are describing, reaches forward towards the head as far as the 
ninth articulation of the back ; in other words, a portion of it lies 
beneath the three last abdominal divisions. It will be recollected 
that the gullar pouch reaches below the fourth articulation of the 
back, and that the whole number of divisions in the vertebral 
column in the genus calymene, is twelve; we have therefore 
discovered in these fragments almost the whole of the inferior 
surface, except the portion which lies below the five articulations 
of the back commencing with the fifth from the buckler or shield ; 
What we shall offer in regard to this portion of the animal must 
be merely hypothetical, or founded on certain analogies of struc- 
ture which probably existed between living crustaceous animals 
and the fossil remains of such as inhabited the most ancient seas. 
Some of our fragments, we think, exhibit a transverse section 
of our trilobite, showing the position and figure of the abdominal 
Cavity which once contained a portion of the viscera of the ani- 
mal. One of the sections is through and parallel with the sixth 
articulation of the back: by this means we have discovered that 
