The Fauna and Flora of the Silurian Period, 523 



distribution of every species known to have existed in the Silurian 

 seas of any area on the globe. The genera are alphabetically ar- 

 ranged under their Sub-kingdom, Province, Class, and Order. The 

 family is omitted, which we regret, this being an important feature 

 in zoological classification. The author of each genus, and date of 

 publication of name, with important synonyma, is given in every 

 case where necessary. An alphabetical order is followed in the regis- 

 tration of the species, which are in every instance stratigraphically 

 placed in one or other, or all of the sub-divisions in which they occur 

 in the British, American, Bohemian, Swedish, Norwegian, or Kussian 

 systems — initial letters in this first column, headed Sub-division, 

 designating the particular horizon in any given stage (in the above 

 systems) in which the particular species is found. The column headed 

 Genera, Species, and Author is followed by three others, termed 

 stages. Lower, Middle, and Upper, expressive of the sub-division of 

 the Silurian system into these three natural life-groups. In each of 

 these columns also occurs the geographical position of the particular 

 species, thus enabling the student to fix the locality and distribution 

 of the forms, and so mentally to re-people with life these old ma- 

 rine areas ; for geographical distribution is at least equal to if not 

 of greater importance than stratigraphical position ; the former 

 determines its place in space, the latter in time — the one its lateral 

 extension over a given sea-bottom, the other its vertical duration or 

 length of specific life. At the close of the analysis of the genera 

 and species of each order is appended a generalized geographical 

 summary, showing the distribution of the genera over the globe. 

 The advantage of these tables cannot be estimated until used. The 

 order Trilohita alone (pp. 72-74) amongst many others commends 

 itself to our notice. The table contains every known genus (no fewer 

 than 126) named in alphabetical order, and also gives their appearance 

 in the several localities, no less than 42 parts of the globe being tabu- 

 lated to receive this group, viz. 24 in America, and 18 in Europe 

 and Australia. The genus Calymene occurs in 32 out of the 42 areas 

 named ; Cheirurus in 26 ; Illcenus in 30; Phacops in 26 ; AsapJins in 23 ; 

 AcantJiopygce in 1 ; Cyphoniscus in 1 : the remaining 120 in every pro- 

 portion. All the orders of the animal kingdom known in the Silu- 

 rian rocks are treated in the same way. 



It is the tabulation of such individual facts that leads to high 

 generalizations, and a positive knowledge of the distribution and 

 nature of life over the globe, and renders it in our power to re-people 

 and restore lost continents, marine areas ; to map out geographical 

 outlines, and to show the probable depth and shape of palaeozoic 

 seas : to understand those groups and communities of life, those 

 local colonies, and the missing links in time which perplfex the 

 palaeontologist at every stage of his investigation, especially in the 

 Silurian regions of Wales, Bohemia, Scandinavia, Spain, Canada, 

 and America. Fifty pages of facts and observations herald the 

 Table itself, these not only explain the use of the Thesaurus, but 

 they forecast and lay down in short and terse paragraphs some of the 

 grand deductions that may be arrived at, through the mass of material 



