Dr. J. J. Bigsby on the ' Thesaurus Siluricus.' 291 



This 'Thesaurus' contains 7553 species, and therefore gives 

 abundant scope for profitable study ; but probably it does not give 

 the tithe of the whole Silurian life yet lying buried in the wilds of 

 the Arctic Circle, of Hudson's Bay, Labrador, the two Americas, 

 Scandinavia, Australia, India, &c. &c. The more accessible countries 

 frequently, to this day, yield new forms, although the search for 

 them is capriciously and idly conducted, and is dependent often on 

 the accident of a new public work or the presence of a competent 

 observer. Many \mdescribed species are lying in local museums, 

 still more in the great collection at Prague in the possession of a 

 high Ecclesiastic in that city. Owing to the enlightened persever- 

 ance of M. Barrande, a few small parishes close to Prague have 

 yielded nearly one-third of the whole earth's Silurian remains within 

 present knowledge ; and the greater part of these are not met with 

 elsewhere. How wonderfully rich must be the universal Silurian 

 fauna! What a splendid promise to the future explorer! 



The * Thesaurus ' is in the form of a Table. After mentioning the 

 genus (taken alphabetically), its author, and the date of its esta- 

 blishment, the species are successively named, and treated of under 

 four or more heads, along one and the same ruled line. First comes 

 the part of the stage in which it occurs, then, in a given order, its 

 author and locality, or localities, in the column indicative of its 

 proper stage. 



More information is thus conveyed, it is believed, than by any 

 other form of Table. The summary which is appended to each order 

 shows some of the organic relations of the Silurian system in Europe 

 and in America to each other ; it shows, too, how very little we know 

 as yet of this epoch in Asia and Africa ; and, among other things, it 

 tells us the numerical strength of the genera. 



Permit me now to lay before the Society a few facts drawn from 

 the mere surface of the 'Thesaurus,' and only in the way of sum- 

 mary or brief remark, in order to suit the purpose of this evening. 

 Much more than this the careful registration of more than 50,000 

 facts has prevented me from doing. 



The Table A gives the numerical amount of the Silurian flora and 

 fauna as known in the years 1856 and 1866 respectively. 



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

 from the * Thesaurus Siluricus,' shows that within the last ten years 

 the number of known species has more than trebled. 

 * Morris, Cntal. p. 302. 



