Description of several new Trilohites. 347 



and a good deal depressed. The breadth of the fragment is one 

 inch, and the length nearly half an inch. 



1 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. It was accompanied by five specimens of 

 the C. Boothii, some of which were coiled up in the manner of the 

 Calymene ; the leaf-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 articulation, where they fin- 

 ished in a rounded termination. 



Trimerus Jacksonii. Green. 



Clypeo? corpore convexo; cauda suborbiculari, costis lateralibus, 

 abdominis, hneatis. 



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. Jackson, whose researches in fossil zoology 

 will continue to illustrate many obscure departments of the science. 



AsAPHus Trimblii. Green. 



Clypeo ? Corpore depresso ; costis planis, parte marginali vix 

 membranacea ; cauda rotundata ? brevi. 



