Description of several new Trilobites. 345 
our specimen is not entirely perfect, this number probably includes 
the whole. The middle lobe is quite prominent; is nearly equal in 
breadth for about two thirds of its course, and then gradually tapers 
to an obtuse tip. Most of the ribs, or'costal arches, are, in our spe- 
cimen, beautifully distinct. There is a little furrow scooped out of 
the upper surface, commencing at the middle lobe and terminating 
near their outward extremities, which are rounded and separated 
from.each other, forming on the sides of the animal a denticulated 
line. Beyond these costal arches, there projects a second series of 
shorter ribs; these commence between the outward extremities of the 
first series, and gradually widen towards their termination. These 
appear intended to support a membranaceous expansion round the 
body. Unfortunately our specimen is rather obliterated on the sides, 
but still small curved spinous prolongations, may be seen in some 
places to terminate the second series of ribs, and will probably be 
found, in more perfect specimens, to project beyond the lateral mar- 
gin of the abdomen on both sides. 
The caudal end is very peculiar. The last five costal arches of 
the tail, terminate abruptly in a narrow membranaceous edge, which 
appears to be continuous with the expansion that surrounds the body. 
Its external border is finely ornamented with five leaf-like scollops 
on each side ; the points of the leaves are free, and all curve to- 
wards a smaller.leaf or lobe, which originates from the central por- 
tion of the tail or terminal joint of the vertebral column. At the 
fifth costal arch, counting from the tail towards the head, where the 
leaf-like appearance of the caudal membrane commences, the sec- 
ond series of ribs, which rise between the extremities of the costal 
arches, terminates. In our specimen, but three of the leaf-like 
scollops on one side remain perfect ; the origin of the other two is, 
however, very obvious. 
This magnificent trilobite was found near the town of Hootingice, 
in Huntingdon County, Pennsylvania, by Professor James C. Boorn, 
to whose kindness I am indebted for an opportunity of describing it. 
The specific name is given in justice to the discoverer, whose emi- 
nent skill in geology, mineralogy, and in analytical chemistry, enti- 
tles him to a much higher distinction. 
In the cabinet of my friend, Dr. R. M. S. Jackson, there is a 
fragment of this species displaying the remarkable organization of 
the caudal end, and a person residing at Huntingdon has another 
specimen ; all were found in the same locality. The rock in which 
4 
Vout. XXXII.—No. 2. 
