Remarks on the Trilobite. 33 
_ The anterior edge of the buckler of this species, as has been 
often observed, is marked by a deep groove or furrow, produced 
apparently by the junction of the upper and the under shell at 
this place, and which at first sight looks like the mouth of the 
animal ; indeed, Professor Brongniart calls the elevated ridges on 
each side of this groove the lips. The mouth was, however, placed 
no doubt much farther beneath. These Zips, perhaps, indicate the 
separation of the shell, through which the trilobite crept out, and 
~ left his cast-off covering in the same manner as recent crustace- 
ans leave their exuvie. We know that the Limulus polyphemus 
creeps through a somewhat similar opening, made along the 
whole anterior edge of his buckler.* In all our fragments, which 
exhibit the under surface of the buckler, the lower Jip is reflected 
beneath, so as to form a kind of scroll or rolled edge, extending 
from one side or angle of the head to the other. Beneath this, 
and passing backwards towards the tail, the surface of the shell 
is not flat and horizontal as in the isotelus and Limulus ; but it 
swells up on each side, below the oculiferous prominences, into a 
kind of oval pouch, diminishing in breadth as it recedes, and at 
last terminates in a rounded point, below the second articulation 
of the vertebral column. This is the position of the gullar po c 
or plate, when the animal assumes a cree ping or swimming atti- 
tude ; but when rolled up in the form of a ball, for the purpose 
of defence, then the gullar plate being composed of a single 
Piece, and therefore not contractile, reached below the fourth ar- 
ticulation of the back. Some of our specimens illustrate this 
conformation in a very satisfactory manner. None of our frag- 
ments exhibit fairly the small surface on each side of the gullar 
plate, and the edge of the buckler beneath the eyes. This space 
Was probably slightly concave, and occupied with the mandibles 
and their palpi, as in the genus serolis—the mouth being no 
doubt placed near the rounded termination of the gullar pouch. 
Thus we have at last discovered nearly the whole inferior sur- 
face of the buckler of the genus calymene, a portion which in- 
cludes about one third of the animal. Not the slightest impres- 
sion or other vestige of antenne can be perceived, and we may 
therefore pretty confidently conclude, that this genus of trilobites 
Were destitute of those organs. Professor Demarest, in his his- 
* See Dr. Dekay. Annals of Natural History, vol. 1. 
Vol. xxxvuit, No, 1.—July, 1839, bis. 
* 
