1867.] ' Thesaurus Siluricus,' 375 



Table A.. — Comparative number of species known in 1856 and I8G6. 







zoa. 



fera. 











a 





traca. 1 



oda. 1 





aria. 



C3 



oda. 





ertainJI 







i 



c 



morpho 



!s 

 s 

 2 



nnelida 



ctero- 

 teropod 



olj'zoa. 



oelenteri 



ehinoder 



rilobita 



ntomos 



rachiop 



.S 



s 



[onomy; 



asteropi 



ephalop 



isces. 



c 



3 



Total. 







< 





< 



ffi P- 



PL, 



o 









m 



S 





O 







U 





Prize Essay 



18 



19 





10 



63 





108 



93 



425 



8 



579 



113 



14 



151 



299 



10 



9* 



1995 



Thesaurus ... 



76 



125 



25 



132 



241 



389 



496 



479 



1400 



247 



1408 



446 



136 



•721 



1192 



34 



6 



7553 



This Table, taken from Bronn's Prize Essay published in 1856, and from 

 the ' Thesaurus Silurians,' shows that within the last ten years the number 

 of known species has more than trebled. 



Tlnwersality. 



In the spirit of the following definition, it would appear that the 

 Silurian system is universal— that is, it overspreads the whole earth more 

 or less completely, — and that its component parts were ]aid down in a 

 proximate time, — statements approved by M. Barrande, Bull. n. s. xii. 361. 

 Definition : — "A formation may he considered to he universal when it occu- 

 pies large and small areas in very many ]jarts of the earth, often remote 

 from and even antipodal to each other, when it is always of like strati- 

 graphical relations, is composed of like materials, and contains numerous 

 genera in common^ together with some representative and some identical 

 species'* 



In support of our application of this definition to the Silurian system, the 

 * Thesaurus ' exhibits the widest possible distribution of its fauna — a fauna, 

 it must be remembered, which is pure from admixture with that of any 

 other epoch which might possibly have been progressing at the same time. 



The ' Thesaurus ' contains many examples of the same species being in 

 twenty to twenty-five different countries, large and far apart — the same 

 creature or creatures marking the route from land to land. 



Table B, drawn up under the inspection of Mr. Salter, presents 195 

 species common to regions very remote from each other, some of them 

 being antipodal — a fact which tells the more forcibly from the tenacity with 

 which a large part of Silurian life clings to locality as well as to horizon. 

 179 species are common to Europe and America. Sixty Silurian genera 

 have been brought from South Australia by Mr. Selwyn, the chief Geolo- 

 gical Surveyor of that colony ; and Professor M'^Coy has met with in that 

 country a Siphonotreta, a Phacops, and eighteen species of Graptolites ab- 

 solutely identical with those of North America and of Europe. The Pro- 

 fessor loudly expresses his surprise and dehght. According to M. Bar- 

 rande, Orthoceras hidlatum (Sowerby) is at Melbourne (Australia) and 

 in Ireland, Bohemia, Germany, and Russia. Conocoryphe depressa is both 

 in Wales and Texas, one of the American States. Western Tasmania, the 



^ Morris, Catal. p. 362. 



