CHAPTER XLVII. 



TRILOBITES OF THE SILURIAN SYSTEM. 



General view of Trilobites. — Their geological range. — Trilobites of the Ludlow and 

 Wenlock Formations, or Upper Silurian Rocks, PI. 7., PI. 7 bis. & PI. 14. — 

 Trilobites of the Caradoc and Llandeilo Formations, or Lower Silurian Rocks, 

 PI. 23., PI. 24. & PL 25. — Structure and Affinities of Trilobites. 



THE natural history of the fossil crustaceans called Trilobites is still imperfect. Though 

 unable to remedy this deficiency, I hope to effect my chief object, by presenting correct 

 sketches of such species of these animals as have been found in the Silurian Rocks of 

 England and Wales, and by explaining the order in which they lie in the strata. 



These bodies have been noticed by numerous writers from the year 1699, when our 

 countryman Lhwyd or Lloyd first described them, to the present time; including French, 

 Swedish, German, Russian and American authors. Linneeus considered them to be 

 insects, and named a remarkable species Entomolithus paradoxus. They were afterwards 

 termed Concha-Triloba, and Knorr, applying this description to the whole family, called 

 them Trilobites, under which name they have been generally known. Brongniart had the 

 merit of being the first to render them serviceable to the advancement of geology, not 

 merely by pointing out their place in the animal kingdom and by dividing the family 

 into genera and species, but also by endeavouring to show what species were peculiar 

 to different deposits. My wish is chiefly to carry out the geological views of M. Bron- 

 gniart, by adapting them to the present state of knowledge ; for as at the period when 

 he wrote (1822), no one had attempted to systematize and classify the older fossiliferous 

 rocks, so it was impossible, even for one who like himself, united the powers of a na- 

 turalist and geologist, to draw correct inferences concerning the relative age of these 

 fossils. 



It is probable that the generic divisions of this family will hereafter be much altered, 

 and that a nomenclature founded on natural characters will be adopted. In the mean- 

 time I shall, as far as possible, adhere to that of Brongniart, merely attaching new 

 names to such forms as have not previously been published. Every naturalist is opr 

 posed to the unnecessary use of synonyms, and hence in common with French and 

 English geologists, I see no reason for abandoning the well-known term Trilobites, to 



4 N 



