2^2 
The Dudley fossil, or that species of this fossil which is found at Dud- 
ley, in Shropshire, is evidently the upper covering only of the animal, 
and appears to have been of a crustaceous nature. It is of an oblong 
ovate form, convex, and surrounded by an uninterrupted border. The 
head is large and gibbous, and divided longitudinally into three parts : 
the middle one rounded, gibbous, and rough, having at its posterior 
part two round projecting knobs, and just before these two smaller. 
On each side of this body is a triangular surface, from the centre of 
each of which proceeds a valvular projection, which, from its form, 
appears to have been capable of being occasionally opened or closed. 
I acknowledge that, in the specimens which I possess, I am unable 
to discover the reticulated surface of the eye of this animal, of which 
many have spoken. Instead of this, I only find the lunated valvular 
projection, by which, it seems, the eye of the animal might be 
occasionally covered or exposed. A magnified representation of this 
part is given Fig. 14, a. 
The back is formed of strong, convex, triarcuate segments, varying 
in number with the size of the animal, and diminishing in size, as they 
approach the caudal termination. These segments are more raised 
in their middle than at their sides ; and in the recent animal, the 
superior, by sliding over the inferior ones, allowed the animal to 
make very considerable changes in its form, by extending or con- 
tracting itself, as is shown Plate XVII. Fig. 11 and 14. The tail is 
obtuse, and without any appendage. In no specimen has the under 
part of the animal been seen, consequently nothing can be said 
respecting the structure of this part, its legs, &c. 
The Derbyshire trilobite differs from that of Dudley in being 
narrower, and particularly so at the upper part ; in not having the 
four tubercles at the posterior part of the head, and in having the 
dorsal segments marked with a line of minute tubercles. Mr. Martin 
has given a representation of the reticulated surface of the eye in 
this animal. 
