Description of several new Trilobites. 347 
and a good deal depressed. The breadth of the fragment is. “one 
inch, and the length nearly half an inch. 
I received this fossil from my friend, Dr. R. M.S. Jackson, of 
Alexandria, Huntingdon County, Pa. It occurs in a soft ferrugin- 
ous slate, through which some sparkling particles of iron pyrites are 
sparsely disseminated. Jt was accompanied by five specimens of 
the C. Boothit, some of which were coiled up in the manner of the 
Calymene ; the Jeaf-like lobes of the caudal membrane, in two of 
these specimens, were smaller than the middle leaf, and the outward 
angles of the buckler in one were perfect, extending down the sides 
-of the animal, to the fourth abdominal er where they fin- 
ished in a rounded termination. 
Trimerus Jacksonit. Green. 
Clypeo? corpore convexo; cauda sishorkicabar: costis lateralibus, 
abdominis, lineatis. 
I have in my cabinet five or six specimens of this species, but they 
are all portions of the caudal end. ‘The most perfect fragment con- 
sists of nine articulations of the middle lobe of the back, with eight 
costal arches. ‘The middle lobe is regularly conical and much flat- 
tened, all the joints being broad and smooth on their upper surface. 
The ribs of the sides are also broad, but they are strongly marked 
by a raised line running through the middle of each; this raised line 
appears to characterize all the lateral ribs of the body, and where the 
crustaceous shell remains attached to the fossil, which is evident in 
two or three instances, this line is very distinct and peculiar. The 
grooves between all the joints are narrow and very slight depressions. 
The tail is rounded. 
This species resembles a good deal the T. platypleurus, but the 
raised line on the upper surface of the ribs, will be sufficient at once 
to distinguish them from each other. It occurs in a hard, compact 
blackish limestone, in Huntingdon County, Pennsylvania. From 
the same locality I have the head of a Trimerus, which no doubt 
belongs to one of this species, but until it is found united to some 
other portions of the animal, its description must be deferred. The 
specific name of this trilobite I have given in compliment to the dis- 
coverer, Dr. R. M.S. Jacxson, whose researches in fossil zoology 
will continue to illustrate many obscure departments of the science. 
Asarnus Trimblii. Green. 
Clypeo? Corpore depresso; costis planis, parte marginali vix 
membranacea ; cauda rotundata? brevi. 
