INTRODUCTION. xiii 



These species were, at this date, mostly published without illustration, but 



figures of these and a few additional Devonian species were given in the 

 Illustrations of Devonian Fossils, in L876. 



The following authors have published descriptions or notices of the American 



Devonian Trilobites, and full reference to their works will be found under the 

 generic and specific synonymies : 



The other orders of the Crustacea have only more recently attracted the 

 attention of American writers. The Xiphosura have been discussed by Wil- 

 liams and Packard; the Eurypterida, by Hall and Claypole; the Phtllocarida, 

 by Hall, Whitfield, Clarke, Packard, Beecher, Woodward and Jones; the 

 Decapoda, by Whitfield; the Phvllopoda, by Clarke, Packard and Jones; and 

 the Cirripedia, by Whitfield and Clarke. 



II. Classification. 



In the discussions of the species, it has not seemed advisable to accord a 

 strict adherence to any given system of classification The Trilobites, which 

 include the larger and, for the geological student, the most important part of 

 the work, stand first in order of treatment ; the other orders of the sub-class 

 to which they belong, being considered in the latter portion of the work. In 

 the introductory discussion of the genera the same order is followed. 



The classification which has been adopted, with modifications, for the purpose 

 of the work, is the following: 



*It is understand that a "Bibliography of the Palaeozoic Crustacea." by Li.-ut. Vbgdes, is read] for press 

 at the present writing. 



