100 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
retractor muscle of the polypide inserted on the median axis of the zooecium assures 
(lie symmetry of the opesium; moreover, there is no ocivell. 
The spinous processes are of the same nature as those of the, genera Hemisep- 
tella Levinsen, 1909, and Cupularia Defrance, 1821. but they are very inconstant; in 
fact, they have not been noted on the recent specimens, nor are they very frequent 
on the fossils. On the contrary, the serrate denticle is rarely found in the fossil 
examples. 
ACANTHODESIA SAVARTII Audouin, 1826.’ 
Plate 21, figs. 2-4. 
3826. Flustra savartii Audouin, Explication sommaire des planches de l’Egypte et de la Syrie, 
in Savigny’s description de l’Egypte, Histoire Naturelle, vol. 3, Paris, p. 240, pi. 10, 
fig. 10. 
3907. Membrampora savartii Canu, Bryozoaires des terrains tertiaires des environs de Paris, 
Annales Paleontologie, vol. 2, p. 6, pi. 3, fig. 1. 
3 908. Membrampora savartii Canu, Iconographie des Bryozoires fossiles de l’Argentine, 
Anales del Museo Nacional de Buenos Aires, vol. 17, p. 252, pi. 2, figs. 5, 6. 
3909. Membrampora savartii Waters, Reports on the Marine Biology of the Sudanese Red 
Sea, XII, Journal Linnean Society, London, vol. 31, p, 137, pi. 11, figs. 8-13. 
1913. Membmnipora. savartii Waters, Marine Fauna of British East Africa and Zanzibar. 
Bryozoa, Cheilostomata, Proceedings Zoological Society London, 1913, p. 486. 
1914. Membrampora savartii Osburn, The Bryozoa of the Tortugas Islands, Florida, Publi- 
cation Carnegie Institution of Washington, No. 182, p. 3941. 
Measurements . — Opesia 
|Ao=0.26-0.32 mm, 
j lo= 0.20-0.26 mm. 
Zooecia 
[Z„3=0.36-0.44 mm. 
i lz= 0.18—0.36 mm. 
Variations . — The American forsil specimens are unilamellar and incrust other 
bryozoa, chiefly the Cellopores. After rubbing away the zoarial surface we have 
observed only one distal septula. The micrometric variations between one specimen 
and another are considerable. Our specimens correspond exactly to those from the 
environs of Paris, and are almost the same as those from Egypt and from the Eng- 
lish Crag, but they differ a little from examples dredged in the recent seas. We 
have figured the extreme forms, but our fossils show all of the intermediate stages. 
The opesial denticle is rarely observed on the fossils on account of its very great 
fragility. Nevertheless, these denticles are very clearly preserved on a specimen 
from the Vicksburgian of Jasper County, Mississippi' (fig. 4). 
The vigor and resistance of this species is extraordinary. Quite cosmopolitan 
in the existing seas, it was present even in the Eocene seas. Unfortunately, we are 
still ignorant of its larval system. It appears sensitive to bathymetric variation, 
implying an elementary hydrostatic system, and the absence of powerful means 
of oxygenation. 
O ccurrence .— Vicksburgian (“Chimney rock” of Marianna limestone): Thi’ee 
miles southeast of Vosburg, Jasper County, Mississippi (rare) : 1 mile north of 
Monroeville, Alabama (very common). 
1 Savigny having become blind, the explanation of his plates was prepared by Audouin in 1826 
Savigny’s plates were published in 1812. 
