82 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



opesium measuring 0.72-0.80 mm. by 0.40 mm. The Cretaceous specimens differ 

 from those of the Vicksburgian in having the opesia finely cremilated. Moreover, 

 some of our specimens branch unilaterally. However, these differences can be 

 proved to exist in the same species. It should be noted that there is no basal 

 olocyst in this species: the lateral walls alone of each zooecium are calcified. 



Occurrence. Vicksburgian ("Chimney rock" of Marianna limestone): One 

 mile north of Monroeville, Alabama (rare). 



Geological, distribution-. Senonian of England; Daman of Denmark (Lang, 

 1014). 



No. 642-29, U.S.N.M. 



Group MEMBRANIPORAE Canu and Bassler, 1917. 



1917. Membraniporae CANU and BASSLER, Synopsis of American Early Tertiary Cheilos- 

 torne Bryozoa, Bulletin 06, United States National Museum, p. 9. 



hii (iiiinloiiiif/il timl <-liixxi/i<-<it<nii I. ISDN. WATERS, Observations on Membraniporldae, 

 Journal Liuueau Society, London, Zoology, vol. 26, pp. 656, 691, pis. 4719. 1900. CALVET. 

 Contribution a 1'liistorie n:\turelle des Bryozoaires ectoprorti-s inarins, Travaux 1'Institut 

 de Zoologie de ITniversite de Montpelier, Mem. No. S, p. 262, pi. 10. 1900, CANU. 

 Revision des Bryozoaires dn cretace figures par D'Orbigny, Cheilostomata. Bulletin Geo- 

 logique Societe France, vol. 28, p. 353. 1903, NORMAN. Notes on the Natural History of 

 East Finmark, Annals and Magazine of Natural History, ser. 7, vol. 11. p. 584. 1909, 

 LEVINSEN, Morphological and Systematic Studies on the Cheilostomatous Bryozoa, p. 143. 

 1913, WATERS. Marine Fauna nf British East Africa and Zanzibar, Bryozoa, Cheilostonmta, 

 Proceedings Zoological Society, London, pi. 71, fig. 1. 



This very large group is too heterogeneous to be considered as a single family; 

 indeed it is certain that the genera classified here at present will ultimately be 

 assigned to many families. Unfortunately we are ignorant of the larvae, and 

 researches upon the anatomy of these forms have not been made. 



The first attempt at classification was made by Waters in 1898 in his excellent 

 work on the Membraniporidae. This author defined 14 groups which for the most 

 part are absolutely natural and which should be considered as distinct genera. We 

 have had frequent occasion to refer to this publication. 



Canu's researches in 1900 were quite incomplete, as they were limited to the 

 Cretaceous species in which most of the specimens were devoid of ovicells. This 

 author then considered chiefly the interzooecial avicularia. 



The work of Norman in 1903 is based for its most part upon the presence or 

 absence of the dietellae and upon the number of septulae. This author established 

 a number of natural genera. 



The material upon which our present researches are founded is most abundant 

 but as it is impossible to establish a satisfactory nomenclature with fossils alone. 

 we must be content to utilize the works of our predecessors. We have studied 

 especially the ovicells and their relations to the opercular valve, for these are the 

 organs in closest relation to the larval system. In the following table are listed 

 the genera of Membraniporae with the possible family reference of some of them. 



