NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
269 
THALAMOPORELLA PRIMA, new species. 
Plate So, fig. 14. 
Description , — The zoarium is bilamellar. The zooecia are distinct, elongated, 
rectangular, and their mural rims are intimately united among themselves; the 
cryptocyst is deep, flat, with numerous tremopores. The apertura is orbicular or 
somewhat transverse, the poster is narrower than the anter; it has a large, distal, 
vestibular arch; the polypidian tube is invisible. The onychocellarium is straight, 
oval, narrow, and perforated by a single elliptical orifice. 
Measurements . — Opesium 
| ho— 0.12— 0.15 mm. „ . \Lz=0 . 55 mm. 
[fo=0. 12-0.15 mm. ° 0eCia |fe= 0.35-0.40 mm. 
Affinities .- — Only a few specimens of this species have been found. They are 
difficult to determine for all the species of the genus are quite polymorphic. To 
us the present form appeared to differ from Thalamoporella rosier i Savigny- 
Audouin (1826) in its smaller micrometric dimensions (lz= 0.55 instead of 
0.72 mm.). 
Occurrence . — Uppermost Vicksburgian (Byram marl) : Leaf River. Smith 
County, Mississippi (very rare). 
Hololype. — Cat. No. 64265, U.S.A.M. 
Division III. PSEUDOSTEGA Levinsen, 1909. 
There are no parietal muscles. The hydrostatic system is external; there is 
a special liypostege on each zooecium. 
The families of this division are : 
Membranicellariiclae Levinsen 1909. 
Cellariidae Hincks 1880. 
Coscinopleuridae Canu 1913. 
We are ignorant of the exact working of the hydrostatic system in the species 
of this division. It is probable that the lateral incisions of the opesium, other- 
wise very constant, are in intimate relationship with the entrance or egress of the 
polypicle, for they serve as passage for the liquid of the general cavity in the 
liypostege or vice versa. 
The endoc} r st covers a liypostege. Its presence is often revealed by supple- 
mentary calcareous deposits which may always be distinguished by their irregu- 
larity. 
Other genera certainly belong to this division, but it has not been possible 
for us to class them in the families cited. It would be absurd to create a special 
family for each of them since we lack absolutely the necessary anatomical features. 
Here the opesium being 1- entirely closed by a constant operculum of the same 
form, becomes a real aperture, as in the Ascophora. 
Family CELLARIIDAE Hincks, 1880. 
Bibliography (Anatomical) . — 1900, Calvet, Contribution a l’Historie naturelle de Bryozoaires 
Ectoproctes marines, Montpellier, Mem. 8, pi. 6, fig. 11 ; pi. 8, fig. 14; pi. 10, fig. 4; pi. 11, 
figs. 10, 11, 12; pi. 12, figs. 7, 8, 9; pi. 13, figs. 12 to 18. — 1904. Waters, Itesultats du voyage 
du S. Y. Belgica, Bryozoa (Expedition antarctique beige), pi. 2, fig. 9. — 1909. Levinsen Mor- 
phological and systematic studies on the Cheilostomatous Bryozoa, p. 209, pis, 7 and 8 
