FACTS AND OBSERVATIONS. 



Xlll 



never leaves its native level. The genera possessing recurrent species are placed in the foot-note *. 

 They are taken from the ' Thesaurus '. 



Out of 224 species of Trilobites in Great Britain and Ireland, as known in 1867, thirty-two 

 exhibit some amount of vertical range, or about 14 per cent. ; but two-thirds of these recurrents 

 occupy contiguous stages, and so may only occupy transition-beds. They may all be found in 

 1 Siluria/ 4th edition, pp. 514 &c. 



As my own later- collected materials for ascertaining the relations of Trilobites to their sedi- 

 ments are not yet ready for use, I have formed, from what was known in 1858, the following 

 Table. As the organic material of this Table was taken from ' Siluria/ 3rd edition, and as its 

 sediments have passed under the eye of Mr. J. W. Salter, it may be supposed that considerable 

 accuracy has been attained. 



The sediments are arranged under eleven heads, which is being as minute, and at the same 

 time as comprehensive, as is required. 



TABLE G. Trilobites (British) appearances and their sediments (1858). 



* Trilobite genera possessing recurrent species in the following numbers : 



Acidaspis .... 6 



^Eglina 1 



Ampyx 1 



Aretnusina .... 1 



Asaphus 4 



Bronteus 3 



Lichas 16 



Phacops (exclu- 

 sive of varieties) 15 

 Platymetopus . . 2 



Proetus 10 



Sphserexochus 4 



Sphserocoryphe 1 



Staurocephalus 2 



Stygina 1 



Trinucleus .... 2 



115 



