164 Forty- SIXTH Report on the State Museum, 



natural and useful classification will be found in the present 

 adopted order and arrangement of the genera. Chapters upon 

 the classification and broader relations of the genera are given at 

 the conclusion of the two principal divisions of the work. The 

 succeeding part ii of volume YIII will embrace the discussion of 

 the genera under the several groups just mentioned, and they will 

 be treated essentially in the same manner as in the present 

 volume. The work on the second part is already far advanced ; 

 a large amount of material has been accumulated for study; 

 thirty-six plates have been lithographed, a considerable number 

 of drawings have been made and a large amount of manuscript 

 has been prepared. 



During the interval of more than twenty years from its com- 

 mencement, great progress has been made in the study of both 

 genera and species of the Brachiopoda. The late Thomas David- 

 son, LL. D., of Brighton, whose life had been devoted to the 

 study of these organisms, living and extinct, made important 

 contributions to our knowledge up to the time of his death in 

 1885. Essays toward the structure and classification of the genera 

 were made by Zittel, (Ehlert and Waagen, and communications 

 of no little importance relating to structural characters of genera 

 and species, appeared from all quarters of the scientific world. 



The multiplicity of these communications is indicated in part 

 by the bibliographic tables presented in this volume ; they also 

 show the wide-spread interest in the Brachiopoda, not only among 

 students of biology, in their structure, morphology and taxonomy, 

 but araong geologists, in their value as stratigraphical indices. 

 American students have heretofore labored under a disadvantage 

 in the irregular diffusion of the literature of the Brachiopoda- 

 Much of the European literature is inaccessible except to those 

 workino^ in the vicinitv of extensive libraries ; the American 

 literature is so scattered through scientific periodicals, proceed- 

 ings of various societies, etc., as to be frequently inaccessible. 

 Furthermore, while the more general treatises of Zittel and 

 CEhlert may be in the hands of many, the greatest of all works 

 upon the subject, that of Thomas Davidson, is beyond the reach 

 of but a very few. 



With this volume, therefore, is presented, especially to Ameri- 

 . can students, the first part of " An Introduction to the Study of 



