merits marked with a line of minute tubercles. Mr. Martin has given a 

 representation of the reticulated surface of the eye in this animal. 



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, have 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 exa- 

 mined, 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 remains 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 struc- 

 ture: 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 

 4>een disposed in folds, not as in the outer coat, in a transverse, but in a 

 longitudinal direction, Fig. 13, b. 



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