22 Eeviews — Big&hys Thesaurus Siluricus. 



The same author has also constructed another table exhibiting the vertical range 

 and distribution of the Bohemian Trilobites, classified according to the several 

 stages adopted in his own great works upon the Geology and Paleontology of that 

 area; no less than 183 species are thus appointed in time — their distribution in 

 space is chronicled also in the Thesaurus itself, on pages 72*, 72!, 72+, the par- 

 ticulars of every known genus is tabulated, and through it we arrive at the fact that 

 the Silurian rocks of the world contain 126 well-determined genera, and 1640 

 species ; their distribution is given, and summed up for both hemispheres — 4 8 pages 

 of the table is devoted to this order alone. Well may this have been called the 

 " Age of Trilobites^'' by the older authors, for no epoch of the world's history was 

 ever so characteristically typified by a group so peculiar. 



Coeval and cotemporary with, if not preceding in time, the THlobita, stand the 

 Brachiopoda. Every ancient sea of the globe seems to have been largely tenanted 

 by this class of moUusca, the group comprises few genera, but is rich in species, no 

 less than 1635 occurring in 47 genera. The most complete analysis as to their 

 distribution and geographical summary is given of this class from page 8g to 126 

 of the Thesaurus. This order has received more attention from British and Foreign 

 naturalists than any of the mollusca, and no group of fossils have been so well de- 

 termined. The labours and researches of our own distinguished countryman, Thomas 

 Davidson, F.R.S., into this group of mollusca, have, however, surpassed all other 

 authors. From the Cambrian rocks, through deposits of every age to those still 

 forming in modern seas, this order has lived on, though now but feebly repre- 

 sented [only II genera living], 37 having died out. The analytical research of Dr. 

 Bigsby shows us that in the Silurian rocks of the American Continent no less than 

 1 1 20 species are known, and in the Eastern hemisphere, 1672. Of the 47 known 

 genera, 27 are common to the two divisions of the Globe, 14, ^ are exclusively 

 American, and 14 European. 



The Orthida lived in and were distributed through and over no less than 40 

 Silurian areas throughout the Globe, 300 species of this family being distributed 

 through the Lower Silurian beds, and 200 in the Upper. 



Other large genera as — Lingula occur in 29 countries or areas. 



Atrypa „ 28 ,, 



Rhynchonella ,, 31 ,, ,, 



Spin/era „ 30 „ „ 



Penta7nerus ,, 30 ,, ,, 



and by way of showing the wide discrepancy amongst the group (or possibly our 

 want of still more perfect knowledge of their distribution than we at present pos- 

 sess) we may instance such genera as the following, which occur only in few areas : — 

 Ca7?iarium in I country or area. 

 Aulo7totreta 2 ,, 



Eatonia 4 „ 



Eichwaldia 2 ,, 



Meganteris I „ 



Mimtdus I ,, 



Pholidops I , , 



Skenidium I , , 



The Primordial genera Lingiilella and Lingtdepis do not pass to higher stages. 



After carefully working our way through tkhe pages devoted to the history of this 

 Lower Palaeozoic group of Mollusca in " time and space," we are the better able 

 to appreciate highly the labour which the author has gone through, and which has 

 placed before the student, with but few errors, the labours of our ablest Paleozoic 

 Palaeontologists ; prominently among whom must stand the names of Davidson, 

 Von Buch, De Vemueil, Hall, and Billings — whose results are now for the first 

 time brought together and classified. No group so conclusively forces upon us the 

 importance of those considerations which we have already dwelt upon relative to 

 first appearance, duration, migration, and extinction through time. 



Up to the close of the Cretaceous period, this order formed a conspicuous part 

 of the marine fauna of every epoch, and one or two genera are still largely repre- 

 sented in the seas of Australia, etc. 



' Camarium, Eatonia, 'Eickwaldia, Lingulej>is, Pholidops, Rhynchospira, Tropidolepsus, 

 Zygospira, Meganteris, Skenidium, Strophodonta, Trimerella, Rennselceria, Trematospira. 



