Description of a new Trilobite. — 169 
Asapuus Puaryrptecrus.— Green. 
Clypeo ? corpore convexo ; costis latis, planissimis ; parte marginali 
Vix membranacea 3; cauda rotundata. 
I have seen the lower portions only of this trilobite, but the char- 
acters which they present are sufficiently striking and peculiar to dis- 
tinguish it from the other species. Ten articulations of the caudal 
extremity of the animal still remain in a good state of preservation. 
The middle lobe of the back is scarcely elevated above the plane of 
the lateral lobes, and as often occurs in the Asaphs; it has a regular 
conical appearance, the apex of the cone forming the terminal joint 
of the tail. Two or three of the last articulations in our specimen 
are somewhat obliterated. The ribs both of the sides and of the 
middle lobe are broad and very much flattened ; their upper surface 
is entirely smooth, except a slight sulcus near the lower edge of the 
- Gostalarches. The grooves or furrows formed by the joints are nar- 
row and not very deep. ‘The tail is rounded, and the membranace- 
ous expansion or border which is found in most of the Asaphs, is in 
this species but very little developed. In one side it is mutilated in 
our fragment. The body of the animal projects considerably above 
the rock in which it is imbedded, and is therefore very unlike the 
depressed forms of most of the Asaphs; indeed, at first sight I took 
it for a Calymene. 
The rock in which the A. Platypleurus is mineralized, is composed 
of hard, compact, black limestone. A small fragment of another 
Asaph reposes near the one just described. It may perhaps be the 
remains of the young g of that species, though the ribs are much more 
rounded. There is also the joint of a small encrinite adhering to 
one of the costal arches. 
1 am indebted to my young friend, Dr. R. M. Jackson, for this 
and some other trilobites found by bim in Huntington County, Penn. 
Vou. XX XH.—No. I. 22 
