324 PALEONTOLOGY OF ILLINOIS. 



and CYCLOSTOMATA. and to him, therefore, belongs the credit of 

 being the first to delineate the two principal divisions of the 

 GYMNOL.EMATA. His family and generic groups, on the other 

 hand, have little to recommend them, as they are largely based 

 upon the most trivial characters, such as the presence or 

 absence, position and number of the "special pores," complete 

 and incomplete calcification of the anterior wall, while even in- 

 dividual peculiarities or conditions due to age are credited with 

 generic importance. As, however, d'Orbigny is the only author 

 who has sought to account for the entire field of fossil and re- 

 cent Bryozoa, the palaeontologist has been obliged, in the 

 absence of a more natural system, to accept that of this em- 

 minent French naturalist as an indispensible basis. 



With a single exception (Hippothoa inflata Hall,) all the 

 Palaeozoic species known to d'Orbigny, were placed by him in 

 his order CENTRIFUGINES (CYOLOSTOMATA Busk) . None of them, 

 however, really belong there, though true Cyclostomatous Bry- 

 ozoa were not uncommon in some of the Palaeozoic rocks. As 

 instances of the unnatural collocations often found in his sys- 

 tem I may mention Omniretepora (generally supposed to be a 

 synonom for Fenestrella) Archimedipora (Archimedes Leseur), 

 the Fenestellid genera Fenestrella, Fenestrellina, Reteporina and 

 Polypora McCoy, and the ACANTHOCLADIID^E Keratophytes 

 Schlotheim (Acanthocladia King), Penniretepora, Ptylopora 

 McCoy, and Ichthyorachis McCoy. The first is found among 

 the CRESCISIDJE with Heteropora and genera of that type, the 

 second with the TUBIGERHLE, and all the rest among the SPAR- 

 SIVM where they are total strangers. 



Busk's skillfully devised system* has rendered most important 

 service in promoting the study of fossil and recent Bryozoa. 

 For D'Orbigny's CELLULINES he proposed the appropriate name 

 CHEILOSTOMATA, and this division especially, he sought to divide 

 into natural families and genera, taking the zoarial characters, 

 or in other words, the result of the mode of combination of the 

 zocecia, as of the first importance. With such characters as a 

 basis he succeeds in dividing the class into convenient and 

 readily recognized groups, which are particularly adapted for 



* "British Museum Catalogue, 3 pts.," "Crag Polyzoa," Palaeontographical Soc. Pub." 



