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 



