vi PREFACE. 



would be a happy escape from the vain attempt to express them. How can the gift of more than 

 2000 Molluscan species, determined by the first palaeozoic naturalist of the age, be worthily 

 acknowledged ? M. Barrande will be fully content to find his reward in any usefulness of the 

 work he has so largely benefited. 



Under the head of " authorities quoted," there will be placed in the Appendix a list of books 

 and memoirs employed in building up this general view of Silurian life, to which, accordingly, has 

 been given the name of " Thesaurus Siluricus." 



As long as an individual Mollusk remains unregistered it loses a great part of its usefulness in 

 natural history ; and we remain ignorant of its place in Creation ; but even then it may reveal an 

 important fact just as the Trilobite speaks of the Palaeozoic period, and the Nummulite of the 

 Tertiary. 



Until some such record as the present is available, the labours of investigators (many of the 

 greatest are still rejoicing us with their presence) will rest comparatively fruitless. 



It has hitherto not been possible to contemplate widely scattered existences in the aggregate. 

 Many facts have been stored up separately, but generalized truths rarely attained. The work now 

 undertaken has not been yet done for any one epoch not even for the Cretaceous period by 

 Mr. Gabb of California, although he has done much and well. 



The elaborate and highly valuable labours of Mr. Etheridge in this direction, on the Jurassic 

 Fauna and Flora, I am happy to say are only waiting for the printer. There are Societies in 

 London who would do themselves great honour by undertaking their publication. 



The Thesaurus Siluricus deals principally with the external circumstances of the Mollusca, and 

 is in the form of a Table. The different subjects are taken alphabetically. After registering a 

 genus of the Order under consideration, with its author, and the date of its establishment, the 

 species, few or many, are successively named and treated under four or more heads, along one 

 and the same ruled line. First comes the subdivision of the stage in which it occurs ; then, in a 

 given order, its author, and locality, in the column indicative of its proper stage. Immediately at 

 the commencement of this Table is placed the stratigraphy of the principal countries concerned, 

 together with an explanation of the abbreviations used in the Table. 



From this seemingly unattractive catalogue of existences the reader has it in his power to people 

 a multitude of localities and horizons with groups of life as picturesque, and as full of movement, as 

 those which Charles Darwin found in the Straits of Magellan : such groups or communities are 

 plentiful in the palaeozoic strata of New York, Wales, Bohemia, &c. 



Besides the use of the ' Thesaurus ' for reference in the closet and the quarry, it furnishes a vast 

 body of facts leading to generalizations in vital statistics ; it provides a high station from which 

 the student may descry the Silurian populations of the whole earth, as far as they are now known. 

 It assists in tracing the extent, shape, and varying depths of basins. By its aid we compare remote 

 horizons, detect regional affinities and differences, and, moreover, we note the curious changes of many 

 kinds which take place while the epoch is passing through its succession of ages. It will place 

 under examination numberless communities of life, their constituents, wants, habits, migrations, 

 duration, and extinction. The attention of the student is particularly directed to the geographical 

 summaries of life appended to some of the orders. 



The " Thesaurus " contains 8997 species, and therefore is an ample field of study ; but it 

 probably does not tell us of one tenth part of the Silurian life still lying buried in Arctic, Subarctic, 

 and Southern America, in Northern Europe, Australia, India, and many other regions. What a 

 splendid promise to the future explorer ! 



