CORALS AND BRYOZOANS OF THE LOWER HELDERBERG GROUP. 



By JAMES HALL. 



An Enumeration and Description of the Corals and Bryozoans 

 of the Lower Helderberg group ; with references to the 

 plates and figures of species in vol. vi, paleontology of 

 New York — unpublished. 



In the Twenty-sixth Report on the New York State Museum of Natural 

 History, the writer communicated a paper on the " Bryozoa and Corals of the 

 Lower Helderberg Group." This paper was published in pamphlet form, in 

 May, 1874, and in the full Report in July of the same year. In 1877 it became 

 necessary to prepare the drawings of these subjects for the Palaeontology of 

 the State. In commencing this work, it soon became apparent that the previous 

 publication was very incomplete, and that a careful revision would be required 

 for many of those species already described. After a study of the entire group 

 of species, with special instruction given to Mr. Simpson, the draughtsman of 

 the work, I committed them to his care. The species have been critically 

 studied by him, and the drawings have been made with a knowledge of the 

 structure and characters of the fossils. The plates have been lithographed in a 

 very satisfactory manner preparatory to the final publication. 



The results of more recent studies made upon the former collections, and 

 upon others subsequently obtained, have rendered it necessary to modify the 

 expressions regarding some of the species previously described, and to designate 

 a considerable number of new species. The revision of the previous paper, 

 together with the descriptions of the new species here included, give an expres- 

 sion of our knowledge of these groups of fossils, up to 1878. 



In the enumeration of the species, I have considered it advisable to make 

 reference to the numbers of the plates and figures, as already arranged and 

 lithographed for the volume of the Palaeontology which will contain the final 

 descriptions. 



# * # The fossils included in this enumeration are designated as Corals and 

 Bryozoans — the line of demarcation between the two classes, in the genera 

 Ch^tetes, Trematopora and Callopora being at the present time not 

 satisfactorily determined. 



