PLATYCRINIDiE. CYATHOCRINUS. 67 



the Devonian seas became extinct before the mountain hmestone deposits began to accii- 



mnhxte, so that, with one or two exceptions at most, each system of ancient rocks lias 



its own peculiar species of crinoids, none of wliich occur in deposits either okler or 



newer than the group in which it first appeared. 



Sir Roderick Murchison at page 206 of his work on Russia and the Ural Mountains 



makes the following observation relative to the occurrence of one sj)ecies of Cyathocrinus 



in the Permian strata. 



"The Crinoidea are extremely scarce, and of seventy to seventy five species which 



inhabited the carboniferous seas, one only, the Ci/athocriniis planus (Miller) lived during 

 the Permian epoch. Even this solitary species is extremely rare and we are as yet 

 unacquainted with it in Russia". 



Sir Roderick does not state the evidence on which the opinion as to the Ci/athocrinus 

 planus occurring in the Permian system is founded. It is true that Prof. Sedgwick in 

 the Transactions of the Geological Society, vol. 3, second series, page 126, states that 

 portions of columns of two species of crinoidea are found in great abundance in the 

 quarries of Magnesian limestone near Humbleton; and also that specimens from Humble- 

 ton and T\-nemouth had been examined by Mr.Miller, and were referred to the C. Planus. 

 It is almost needless to repeat that considerable difficulty and doubt must of necessity 

 prevail in referring portions of columns to particular species unless the structure of the 

 whole column from its base to the apex is well known, or has been seen attached to the 

 body of the crinoid, it is therefore far from certain that the Cplaniis lived during the 

 Permian epoch. 



