Beviews — Bigsby's Thesaurus Siluricus, 21 



of Gasteropodous mollusca, indicating maturity in time and a fitness of conditions- 

 for organic life — may seem remarkable — but it will appear even more so if we 

 examine into the life-history of the Cephalopoda, which, during the same epoch, 

 numbered some 1400 species ! 



Trilobita. — This is the second group selected and treated of by the author, and 

 necessarily so, for they are the medals and type of life peculiar to the seas of 

 Silurian time, and are almost universally spread over the globe. We find 1 19 genera 

 and 1680 species occupying the rocks of no less than forty-four countries ; 74 genera 

 and 1000 species are primordial, and 46 of these 74 [so called] primordial genera 

 are not known above this stage, no one (so far as we know) of the 23.5 early 

 species, recurring in the overlying Caradoc of any country, or in the Trenton beds 

 of America — and, according to the Thesaurus, we arrive at the fact that " a pri- 

 mordial form has usually a considerable vertical range within its native stage, and 

 there only ; "^ and Barrande and Bigsby, through the labours of Hall and Billings, 

 and the American Palseontologists, determine from materials now collected together 

 in the Thesaurus, " That life began earlier, and more abundantly in the valley of the 

 St. Lawrence and Mississippi than in Europe. " This we may qualify, however, 

 through negative evidence, from want of more complete knowledge of the extent 

 and nature of the rocks once occupying the area west of St. David's Head and the 

 south of Ireland, and, indeed, the whole bed of the Atlantic, and, perhaps, also 

 the Bay of Biscay, — for daily we are adding new facts connected with the older and 

 underlying rocks below the "Lower Lingula flags " of the South Wales Promontory; 

 and what do we yet know of the "Western promontories of Ross and Sutherland 

 and the Hebrides, or those rock -masses termed the fundamental Gneiss of Murchi- 

 son. Could we but restore or examine these sub-atlantic deposits in South Wales 

 and North-west Scotland, the St. Lawrence basin and Britain would, probably, 

 be one in age and life, one in time and condition. Research tells us that the pri- 

 mordial Trilobites alone, in the western valleys of America, number some 40 

 genera and 200 species, and these assembled in two similar foci or centres, 

 Wisconsin and Lower Canada. Sweden has its own primordial fauna, represented 

 by 18 genera and 56 species; Bohemia, 8 genera and 28 species ; Great Britain 

 and Ireland, 1 1 genera and 33 species. 



The author of the " Thesaurus" determines that out of the 57 American genera, 

 16 are exclusively localised in that hemisphere, and of the 116 European genera, 

 69 are not known elsewhere ; the work also shows that 31 genera have each only 

 one species, and that only one genus of the 31 occurs out of its native area, — 

 Polyeres (Bohemia and France); and the largest Genera have been subjected to the 

 widest dispersion^ thus — 



Calymene, with 61 species, is known in 29 regions, 



5 5> 24 )) 



» 5> 20 ,, 



1' 5» 21 ,, 



> 11 20 ,, 



1 11 2o „ 



» 11 14 )) 



.) )> 18 ,, 



We know also that the same species in large genera inhabited many regions 

 widely separated, thus proving their dispersion and distribution over great areas. 

 The British Calyt?tejte Blimienbachii and C. senaria, inhabited 1 7 regions, from the 

 Trenton Limestone of America to the Wenlock of Wales, Russia, Sweden, Nor- 

 way, Esthonia, England, Ireland and Scotland. Encriminis punctahis 8, and in 

 two quarters of the globe. Bumashis {IllcEmis) Barriensis in 10, and all in the 

 Upper Silurian deposits from Sardinia to England, and the American continent. 

 In the year 1858, 126 species of Trilobites were known to Great Britain and Ire- 

 land, but in the new (4th) edition of Sir Roderick Murchison's " Siluria," is 

 catalogued 224 species, or one hundred additional forms have been added to the 

 Silurian fauna in lO years. 



At page 71 of the "Thesaurus," Barrande has enumerated for Dr. Bigsby no 

 less than 79 species of Trilobites discovered in the Bohemian basin since 1852 



We do not here discuss the breaks in time either physically or palaeontologically ; it is too 

 large a subject. 



Lichas, 



82 



Fhacops, 



96 



Dalmannia, 



54 



Cheiruriis, 



86 



IllcBims, 



ICX> 



Isotehis, 



7 



Froetus, 



66 



