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 crenulatcd. 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 
olocvst 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; Danian of Denmark (Lang, 
1914). 
Plesiotype. — Cat. No. 64229, U.S.N.M. 
Group MEMBRANIPORAE Canu and Bassler, 1917. 
1917. Membraniporae Canu and Bassler, Synopsis of American Early Tertiary Cheilos- 
tome Bryozoa, Bulletin 96, United States National Museum, p. 9. 
Bibliography ( anatomical and classification) . — 189S, Waters, Observations on Membra niporidae, 
Journal Linnean Society, London, Zoology, vol. 26, pp. 656, 691, pis. 47-49. — 1900, Calvet, 
Contribution a l’historie naturelle des Bryozoaires ectoproctes marins, Travaux lTnstitut. 
de Zoologie de l'Universite de Montpelier, Mem. No. S, p. 262, pi. 10. — 1900, Canu, 
Revision des Bryozoaires du eretace figures par D’Orbigny, Cheilostom'ata. Bulletin Geo- 
logique Socigtd France, vol. 28, p. 353. — 1903, Norman. Notes on tbe 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 of British East Africa and Zanzibar, Bryozoa, Cheilostomata, 
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 Avork 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. 
