Description of new North American Trilohites. 337 



sions on each side of the cheeks, commencing near the protuberan- 

 ces on the front, and running towards the lateral edges of the buck- 

 ler. The posterior border of the buckler where it joins the lobes of 

 the abdomen, is marked by a transverse groove, nearly continuous 

 with the lower transverse furrow on the front ; this groove at its com- 

 mencement, appears to bifurcate outwards. 



The abdomen and tail cannot be distinguished from each other. 

 There are seventeen distinct articulations in both. The middle lobe is 

 very convex, and is separated from the lateral ones, by a deep chan- 

 nel ; it gradually tapers to an obtuse tip. In our specimen there is 

 a small part of the tail of another trilobite deposited in this place, 

 which at first sight appears to be a dislocated fragment of our animal. 



The lateral lobes are flattened ; the costal arches are very dis- 

 tinct near their insertion, and for about half their length, but towards 

 their free extremities they are a good deal obliterated. There ap- 

 pears to have been a delicate membranaceous prolongation for a con- 

 siderable distance beyond the solid portion of each rib. This or- 

 ganization is very apparent on the costal arches of the tail. There 

 is a deep groove running obliquely over the upper surface of each rib. 

 Length of the fossil about nine inches ; breadth about four inches. 



This remarkable species of trilobite I have named in compliment 

 to our zealous naturalist, Richard Harlan, M. D., who sent me the 

 specimen above described, with the following note. 



Dear Sir, — During my recent visit to Boston, I observed the fine 

 specimen of trilobite which accompanies this note, in the cabinet of 

 Mr. Francis Alger, to whose politeness J owe this opportunity of of- 

 fering you an additional species for your interesting and useful mon- 

 ograph of American trilobites. The present specimen is undoubt- 

 edly American, though Mr. Alger expressed some doubt as to its 

 precise locality. He supposed it to be from Trenton Falls, in the 

 State of New York. I have the honor to be respectfully, 



Your friend, he. 



Philadelphia, March 27th, 1833. RiCHAKD Harlan. 



As the p. Harlani is in flinty siliceous slate, it does not prob- 

 ably occur at Trenton Falls, where the rocks are mostly formed of 

 carbonate of lime. Our species resembles very much the P. Tessi- 

 ni of Brongniart. a representation of which he gives from Prof. 

 Wahlenberg, on Plate 4, fig. 1, which fossil is the old Entomolithus 

 paradoxus of Linne, and has been found only in Westrogothia, at 

 very great depths, " dansles couches d'arapelite alumineux." 



Vol. XXV.— No. 2. 43 



