PREFACE. 
xi 
was carried out so far as the lithographing of about thirty plates, when the 
farther progress of the work was suspended, to be resumed only in the latter 
part of 1888. 
In the meantime the duties of the author had separated him almost entirely 
from this work, and owing to changes, over which he had no control, in 
the organization and management of the State Museum, the collections which 
he had planned to make for use in its preparation had not been made. The 
progress in our current knowledge of the subject, and that recorded in the 
publication of volumes and miscellaneous papers during more than twenty 
years had been enormous, and the undertaking which had been deemed feasible 
in 1867, seemed almost beyond attainment in 1888. The work was resumed 
however, with no other collections immediately available for use, than those 
upon which it had been commenced. In the original plan four plates were left 
for the illustration of the Inarticulata; the present volume furnishes ten 
additional plates, and the illustrations of these forms may be regarded as fairly 
complete, according to our present knowledge. 
The plates which were lithographed at the commencement of the work are 
designated on the upper left-hand margin as “Volume IV, Part II.” Those 
lithographed since 1888 are designated as Volume VIII, and while the illustra¬ 
tions of the first named plates are not always arranged as would have been 
done with later knowledge and more abundant material, it is hoped that the 
intercalation of the new plates may not seriously interfere with the proper 
connection and continuity of the work, or with the facility of reference so 
important to the student. Although the final numbering is XX, the actual 
number of plates in the volume is forty-two. 
The printing of this volume had been completed to the end of the 
Inarticulata, page 183, in March, 1890, when farther progress was suspended, 
from causes over which the author had no control. The printing was resumed 
in the autumn of 1890, and the book was in type to page 304 in February, 1891, 
when its progress was again suspended to be resumed only in April, 1892. 
This delay in publication, which has not in any way been due to the author, 
requires an apology to the scientific public; and those authors who may have 
