2 
BULLETIN" 106, UNITED STATES NATIONAL MUSEUM. 
join him as senior author in the work. Upon his consent, the study, description, 
and illustration of the numerous American species were energetically pursued and 
much progress had been made previous to the outbreak of the great war. This was 
naturally lessened by the civil mobilization of the senior author, but he was still 
enabled to spend a portion of his time upon the work. By the end of 1917, in spite 
of other exigencies arising from the war, the present monograph, comprising over 
700 species of lower Tertiary bryozoa, had been completed and the study of the 
upper Tertiary forms much advanced. In view of the necessarily slow publication 
of a large paleontological work, the authors early in 1917 issued preliminary descrip- 
tions of certain new genera and families, published as Bulletin 96 of the United 
States National Museum, under the title: A Synopsis of American Early Tertiary 
Cheilostome Bryozoa. 
The Tertiary bryozoa belong almost entirely to the two orders Cyclostomata 
and Cheilostomata, the number of the latter being almost double that of the former. 
In North America the Midwayan, Wilcoxian, Claibornian, Jacksonian, and 
Vicksburgian groups contain by far much larger faunas of this class than the suc- 
ceeding rocks. For convenience only, the above-named groups have been designated 
as the Early Tertiary and their bryozoa are described in the present volume. 
The study of the American Miocene, Pliocene, and Pleistocene species has been 
completed and it is hoped that their description can be published in the near future. 
With a very few exceptions all of the type-specimens described and illustrated 
in the present volume are contained in the paleontologic collections of the United 
States National Museum. The Museum catalogue numbers are given in the plate 
descriptions. The station locality numbers of the United States Geological Survey 
are cited on pages 15 and 16. 
The illustrations were prepared by photography, an ordinary 3-inch objective 
being used in a camera with a long bellows. The photographic prints were locally 
strengthened only enough to retain the scientific details when the illustrations 
are reproduced by half tone. It has been found most satisfactory from an 
artistic standpoint to blacken the apertures in many cases; indeed, this is often 
the only retouching that the prints have undergone. 
The plates are arranged according to the five large geological divisions here 
treated — Midwayan, Wilcoxian, Claibornian, Jacksonian, 'and Vicksburgian. 
Under each of these divisions the species are arranged as nearly in biologic order 
as possible. It should be noted, however, that any species which occurs in two or 
more of these divisions is illustrated only under the oldest one. Thus, for example, 
the illustrations of a species occurring in both the Claibornian and Jacksonian are 
to be found only on the Claibornian plates. 
ACKNOWLEDGMENTS. 
In the accumulation of data and specimens for the preparation of. this 
monograph the authors are indebted particularly to the various geologists of the 
