Description of new North American Trilobites. 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. plidomen, and tail cannot he distinguished “from each other. 
There ions in both. The middle lobe is 
very convex, and i is past 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 inc 
This remarkable species of ilobite I have named in conighanen 
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 | 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, &e. 
_ Philadelphia, March 27th, 1833. Ricwanp. Harwan. 
As the P. Harlani is in fiinty 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- 
mi of Brongniart, a representation of which he gives from Prof. 
Wahlenberg, on Plate 4, fig. 1, which fossil is the old Entomolithus 
paradoxus of Linné, and has been found only in Westrogothia, at 
very great depths, ‘* dans les couches d’ampelite alumineux.” 
Vor. XXV.—No. 2 3 
