12 AMERICAN FOSSIL BRYOZOA. [bull. 173. 



a better designation. Prof, James Hall regarded the locality at the 

 Falls of the Ohio as of Upper Helderberg age, but we have fol- 

 lowed Mr. E. O. Ulrich in considering this locality of Hamilton age. 

 Future researches may prove that the Upper Helderberg and Hamil- 

 ton, as now commonly understood, are to some extent synchronous. 



To avoid ambiguit}' we have adopted the term Mississippian for the 

 formations underlying the Coal Measures and overlying the Devonian, 

 and have used the grouping of these formations given b}'^ Williams 

 and Keyes, with some modifications. 



3. In the diagnoses of suborders, families, and genera we thought 

 it advisable to give the number of undescribed species known to us, 

 as it would give a better idea of the mimber of brvozoa known from 

 American Paleozoic strata. , These undescribed species are in the col- 

 lections of Mr. E. O. Ulrich and the authors. 



4. In the list of publications preceding the catalogue of genera and 

 species we have placed an asterisk before those which are of most 

 importance to the student of the bryozoa. The dates we have given 

 do not alwa3^s agree with those on the title-pages. We have given 

 the date of distribution in cases where we know this to be different 

 froui the date of publication. 



CLASSIFICATION^. 



SYSTEMATIC POSITION. 



The earliest investigators of the bryozoa regarded them as plants, 

 but by the beginning of the nineteenth century there was general 

 agreement among naturalists as to the animal nature of these organ- 

 isms, often so plant-like in appearance. For a time their systematic 

 position remained in doubt, and they were uneasih^ shifted from class 

 to class. In 1830 J. V. Thompson published his discoveries. On Poly- 

 zoa, a New Animal Discovered as an Inhabitant of some Zoophites;^ 

 whence most British authors have applied the name Pol3^zoa to these 

 organisms, speedily dignified as a class. Almost simultaneously C. G. 

 Ehrenberg^ separated these organisms as a group of his Ph3^tozoa 

 Polypi under the name Bryozoa; which name became current among 

 Continental authors and seems now gradually superseding Thompson's 

 name also among British writers. For a considerable time the Bryo- 

 zoa, with the Brachiopoda and Ascidia, formed the " subkingdom '' 

 Molluscoidea, but the Ascidia have been removed from this assem- 

 blage, and doubts have arisen whether the points of agreement of 

 bryozoa and brachiopoda are of fundamental importance. The deter- 

 mination of the exact affinities of the bryozoa remains a subject for 

 investigations. 



1 Zool. Researches, No. 5, pp. 89-102, pis. i-lii. 



2 Symbolae Physicse, seu Icones et Descriptiones Aiumalium Evertebratoruni, 1828-1831. 



