CHAPTER Vlll 



TKILOBITA 



Among the many interesting groups of fossils found in the 

 Palaeozoic deposits there is none which has attracted more 

 attention than the Trilobites. As early as 1698, Edward 

 Lhwyd, Curator of the Ashmolean Museum in Oxford, recorded 

 in the Philosophical Transactions the discovery of Trilobites in 

 the neighbourhood of Llandeilo in South Wales ; and of one of 

 his specimens he remarked that " it must be the Sceleton of a 

 flat Fish." In the following year the same writer gave in his 

 Lithophylacii Britannici Ichnogra'phict descriptions and figures of 

 two Trilobites which are evidently examples of the species now 

 known as Ogygia huchi and Trinucleus Jimhriatus. 



Although Trilobites differ so much from living Arthropods 

 that it was difficult to determine even whether they belonged to 

 the Crustacea or the Arachnida, yet one of the earliest writers, 

 Dr. Cromwell Mortimer, Secretary of the Eoyal Society (1753), 

 recognised their resemblance to A2ms (see pp. 19-36). This view 

 of their affinities was adopted by Linnaeus, and has been supported 

 by many later writers. Another early author, Emanuel Mendez 

 da Costa, thought that the Trilobites were related to the Isopods, 

 an opinion which has been held by some few zoologists of more 

 recent times. 



The Trilobites form the only known Order of the Crustacea 

 which has no living representatives. They are found in the oldest 

 known fossiliferous deposits — the Lower Cambrian or Olenellus 

 beds, where they are represented by 19 genera belonging to the 

 families Agnostidae, Paradoxidae, Olenidae, and Conocephalidae. 

 From the variety of forms found and the state of development 

 which they have reached, it is evident that even at that remote 



