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 bo 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 Huntingdon, 

 in Huntingdon County, Pennsylvania, by Professor James C. Booth, 

 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 



Vol. XXXIL— No. 2. 44 



