2 



BRITISH FOSSILS. 



acknowledged in the " Silurian System/' Messrs. Gray and Fletcher, 

 of Dudley, have kindly enabled us to complete the details, and the 

 figures in this plate are nearly all drawn from Upper Silurian 

 specimens, while those previously given, with one exception repeated 

 in this plate, were from the Llandeilo flags of South Wales. 



The genus to which this rather common fossil belongs is highly 

 interesting for the remarkable sculpture of the body rings, which 

 are broken up into a number of prominent swelhngs divided by 

 deep furrows, and have their ends freely extended into sharp points, 

 which are so widely distant from each other, that it would require 

 the animal to roll up to bring them into contact. The tail is made 

 up of a few similar rings, cohering only at their base, and having 

 the ends also free and pointed. The nature of the eyes also is 

 worthy notice, inasmuch as they are covered by a facetted cornea, 

 like that of Phacops caudatus, and not, as in most trilobites, with 

 a smooth one. The facial suture, in this and one or two closely 

 related genera, runs as it does in Phacops, to the outer margin of 

 the head. The shell or crust is strong and calcareous, the furrows of 

 the head well marked ; the hypostome or labrum has a considerable 

 resemblance to that of the genus above mentioned, and the number 

 of rings in the thorax is the same — so that it is almost certain, 

 much as the general appearance resembles Paradoxides, that there 

 is a really close affinity between it and those species of Phacops 

 which have the tail fringed with long spines. 



Description. — One of the largest of trilobites ; it measures oc- 

 casionally 15 inches, and probably more, judging from the propor- 

 tions of the large fragments previously figured* to that of perfect 

 specimens of a smaller size. Those found at Dudley are not 

 above one and a half or two inches long, — specimens from the Mal- 

 verns are much larger. Length to breadth as three to two ; the 

 head occupies fully one third the length, and is a little broader than 

 the body. General form moderately convex, and oblong, but 

 narrowed suddenly towards the posterior end ; the sides of the 

 thorax and tail deeply serrated by the projecting ends of the seg- 

 ments. The animal is sometimes found half coiled up ; the pointed 

 ends of the pleurse closing together and overlapping each other 

 (fig. 2.) 



Head rather more than a semicircle, — the obtuse front project- 

 ing ; glabella gently convex, equal in breadth at the base to the 

 cheeks, above considerably broader, marked with three strong 

 furrows on each side besides the neck furrow, the lowest being 

 * Mem. Geol. Surrey, voLii, pt. 1. pi. 7. 



