F Vil 
far from believing that they will all pass unchanged 
through the ordeal of future and more favorable op- 
portunities for nice discrimination. 
I ought, perhaps, here to mention that some per- 
sons have imagined that in describing the fossil called 
Triarthrus Beckit, (Fig. 6, on the frontispiece,) I 
have mistaken the abdomen for the buckler of the ani- 
mal. Dr. J. Eights, of Albany, first suggested this 
to me, ani he has since published this opinion in his 
interesting account of the recent trilobite discovered 
at the South Skctlands.* Almost any one but little 
accustomed to accurate discrimination, will be apt to 
make the same remark. ‘The three abdominal articu- 
lations of the Triarthrus are very analogous to the 
three plicze or wrinkles, on the middle lobe or front 
of C. Macropthalma of Brongniart, and to those on the 
front of some of the other genera and species, so that, 
judging from this character alone, I was almost led 
to believe that it was the head of the animal, but the 
peculiar direction or course of the grooves or joints, 
_ andespecially the narrow cuneiform appendages to the 
sides, which I have called the lateral lobes, an organ- 
ization so different from any thing I had before seen, 
determined me in the description given in the Mono- 
graph. No other traces of the Triarthrus than those 
which I mentioned have yet, to my knowledge, been 
discovered, and until the whole animal shall be found, 
or some other parts of it be fairly recognized, I can- 
* See Transactions of the Albany Institute, vol. 1. p. 07. 
