PREFACE. 
The completion of the present volume is a partial fulfillment of a promise 
made at the close of Volume IV of the Palaeontology of New York, in 1867. The 
work is presented to the student with a hope that it may prove a useful con¬ 
tribution to science and a helpful guide in the study of that most abundant and 
most important class of Palaeozoic fossils, the Brachiopoda. Originally intended 
to form a supplementary part of Volume IV, the subject has expanded to such 
an extent that two volumes will be required to present the results with a 
reasonable degree of completeness ; and even with this addition some very 
important matter, as the microscopic shell structure, originally intended for 
the work, will have to be omitted from these volumes. 
The study of the Brachiopoda made necessary in the preparation of Volumes 
III and IV, and more especially in the latter, had shown the necessity of sub¬ 
dividing many of the older recognized genera, which had become the receptacle 
for forms having external similarity to the typical members of the several groups, 
but possessing quite dissimilar internal features. The natural disinclination to 
propose new generic terms for members of a class of fossils which had been so 
widely and thoroughly studied in Europe, operated as a restriction in the 
erection of new names. However it became necessary to describe in those 
volumes and in cotemporary papers some thirty-one new generic forms and 
to suggest the necessity for farther separation among other heterogeneous 
assemblages. These studies, made with fairly good collections, and ranging 
through the Silurian and Devonian faunas, could not fail to attract 
attention to the different external aspects and interior characters of 
forms known under the same generic terms, and considered as distri¬ 
buted through all the Palaeozoic formations. Although the genera thus 
far proposed had not been based upon a recognition of their appearance and 
duration in geological time, yet the student could not fail to discover evidences 
