24 
terminate just below the last articulations of 
the abdomen. This lunate surface is com¬ 
posed of a single thick crustaceous plate or 
piece. Beyond this crescent shaped piece, di¬ 
rectly below the vertebral column, there is a 
deep cavity in the under shell of the animal, 
which corresponds in figure and dimensions 
with the gullar pouch or under surface of the 
buckler. By this peculiar mechanism, when¬ 
ever the animal rolled itself into a ball to 
give protection to the soft parts of the ab¬ 
domen, 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 tri- 
lobites only as perfect animals, which are 
found rolled—the others being merely exuded 
or cast off shells, and in such alone, he re¬ 
marks, can we expect to discover the organi¬ 
sation of the inferior surface. Most of the 
fragments from Berkley Springs, which have 
occasioned my present remarks, are found 
