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On breaking the Dudley fossils, the inner surface of their covering 
is found marked with undulating striae, the impressions of which are 
also found on the inclosed matrix. In none of the specimens which I 
have thus broken, or have rubbed down, have I been able to discover 
any remains of an inferior or ventral covering, corresponding with 
the upper one, which has been just described. M. Walch, indeed, 
observes, that no under covering, or plate, has been ever discovered. 
A trilobite is represented in the Memoirs of the Swedish Academy, 
as possessing antennae. This seems to have been the consequence of 
some mistake ; since, in none of the specimens which have been since 
examined, has the appearance of such a part been ever seen. 
Another species of this animal is found in the schistose strata in the 
neighbourhood of Llanelly, in Carmarthenshire. Plate XVII. Fig. 13. 
This differs from the preceding species in two material respects : the 
lateral lobular divisions are nearly three times as wide as the central 
one ; and the outline of the animal approaches much nearer to the 
elliptical than the ovate form. From this latter circumstance, it obtains 
some slight resemblance to a sole, and has therefore been considered 
by some as the petrifaction of a fish of that tribe. The mutilated re- 
mains of this species, in consequence of the fossil being frequently 
severed transversely, have been regarded as petrified butterflies. 
On the remains of one of these I have perceived a very curious 
structure : it is in that part of the fossil which presents itself to view 
on the removal of the external covering, and which was probably the 
cuticle of the animal. Here the form of the parts appears exactly to 
correspond with that of the crustaceous covering, being transversely 
and somewhat obliquely disposed ; but, aided by the lens, the eye 
discovers, that this pellicle is marked by frequent and regular rugae, 
as if the pellicle had been disposed in folds, not as in the outer coat, 
in a transverse, but in a longitudinal direction, Fig. 13, h. 
Another species, the representation of a mutilated fragment of which 
is given Plate XVII. Fig. 16, is a very extraordinary fossil. In this 
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