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Art. III. — Monograph of the Fossil Polyzoa of the Secondary and Tertiary Formations 



of North America. 



By Wm. M. Gabb and G. H. Horn, M. D. 



In the following paper are included descriptions of all the known species of Ameri- 

 can Secondary and Tertiary Polyzoa. The large majority of these descriptions were 

 taken from specimens either in the collection of one of the authors or of the Academy 

 of Natural Sciences of Philadelphia. Where we are unacquainted with a species, we 

 have given the author's description in full. 



Particular credit is due to Mr. C. C. Abbott, of Trenton, N. J., for obtaining for us 

 the fine mass of material, mentioned all through the paper as coming from near 

 Mullica Hill, N. J. We are also indebted to Dr. A. L. Heermann for collecting some 

 marl near Santa Barbara, Cal., which has yielded us over a dozen species. 



We hope that the study of these beautiful little animals will now receive a start in 

 this country, and that persons, having an opportunity, will collect the many unknown 

 species which undoubtedly exist. We shall feel ourselves under many obligations to 

 collectors who will supply us with any of the species in this paper, not described from 

 specimens, or any that may be new, promising to make all due acknowledgments 

 and, if desired, exchange for them. 



No classification of the Polyzoa has been proposed that is entirely without objec- 

 tion. Perhaps the best one is that made by d'Orbigny, in Paleontologie Francaise, 

 Terrains Cretaces, vol. 5. He there divides these animals into two orders — " Bryo- 

 zoaires cellulines " and " Bryozoaires centrifugines." These two orders are character- 

 ized by the mode of increase of the cellules. In the first, the cellules arise from the 

 sides or ends of preceding ones ; in the second, they are arcuate and arise behind or 

 at the base of the older ones. This division is fundamental, and we believe it to be 

 of far greater importance than one founded on the shape of, or appendages to, the 

 mouths of the cellules, as in the arrangement proposed by Johnston in his British 

 Zoophytes, and, in the main, followed by Gray and Busk. Any classification, how- 

 ever, must be considered merely provisional until it can be ascertained to be correct 

 by careful study of the animals ; and there has not yet been a sufficiently thorough 

 examination made of the animals of these two orders, or, as they will probably prove 



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