PREFACE. 



This volume includes the descriptions and illustrations of the Corals and 

 Bryozoa of the Lower Helderberg group ; of the Bryozoa proper, and allied 

 forms, from the Upper Helderberg and Hamilton groups. 



When the study of the Broyzoa was begun, the plan of the author con- 

 templated the production of a work, as complete as possible, to illustrate the 

 structure and relations of this class of fossils from the Lower and Upper 

 Helderberg, the Hamilton and Chemung groups. With this object in view, 

 extensive collections were made from all accessible localities. The drawings 

 were commenced and carried on in accordance with this plan, and the better 

 specimens for the illustration of the Genera and Species were figured, while 

 awaiting other collections to supplement the incomplete material already 

 pos.sessed. In this manner some of the groups (or genera) have been very fully 

 illustrated, while others, for want of better material, have been less completely 

 represented. 



Although considerable collections had been made in preceding years, it was 

 not until 1874 that the author, with the assistance of Mr. R. P. Whitfield 

 prepared preliminary descriptions of most of the Corals and Bryozoa of the 

 Lower Helderberg group, at that time known to us ; which were published in 

 the Twenty-sixth Report of the State Museum of Natural History. At a later 

 date, while the drawings for the illustrations of these species were in progress, 

 and after their completion, a careful review and revision of the species pre- 

 viously described, and of the new material in hand at that time, was made by 



