348 Description of several new Trilobites. 
Our fragment exhibits eleven articulations of the abdomen, and 
nine of the costal arches, all in a good state of preservation. It 
presents another example of the fact, that the ribs of the side lobes 
do not always correspond in number and position with the articula- 
tions of the vertebral column. | 
Like most of the fossil animals of this genus, the head is mutila- 
ted or lost; yet what seems to have been a small fragment of the 
front or middle lobe of the buckler, lies on the rock at a little dis- 
tance from the abdomen. It is marked by two deep curved, trans- 
verse plice or folds. 
The body is much depressed ; the middle lobe is slightly conical, 
and terminates in a very obtuse tip ; its articulations are all regularly 
rounded and smooth. The costal arches are also rounded, and 
without strie, grooves, or pustulations, and have the same breadth 
throughout ; the lower ribs are slightly curved, and they all termi- 
nate very abruptly in the membranaceous expansion. ‘This organi- 
zation of the Asaph is beautifully developed in our specimen ;—the 
membrane is narrow, even and smooth along the sides of the body, 
forming a regular hem or border; at the central portions of the tail, 
it gradually widens and makes a short rounded projection. It is dif- 
ficult to say, whether the whole caudal membrane is entirely perfect 
in our specimen, for there appears to be an acute point in the rock, 
formed by some animal remain, just beyond the rounded end of the 
tail. If this be a part of the animal, then the central portion of the 
caudal membrane is acute, and not rounded. 
fam indebted to Dr. J. Trimsxe, of Huntingdon County, for 
this species. This gentleman has contributed very much to the il- 
lustration of the geology and natural history of the interesting County 
in which he resides, and J take pleasure in calling this species by his 
name. It was found by him not far from his residence, in a buff- 
colored clay slate. I have examined a fine large fragment of what 
seemed to be our present species, in the possession of Professor 
Oxtver P. Hussarp, of Dartmouth College; but as the membra- 
naceous expansion, if it possessed one, is broken off all round the 
body, we could not fully determine the question. It also occurs 9 
yellowish limestone, and was found, in company with the CaLyMENE 
ii, at Juliet, in the State of Illinois. 
The Asaruus Trimblii resembles, in some respects, the A. la- 
ticostatus, but its depressed form, its narrow membranaceous border, 
and the regular breadth of its costal arches, with some other pecu- 
liarities, will on comparison, readily distinguish the two species. The 
