NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
123 
MEMBKENDOECIUM PYRIFORME Cami and Bassler, 1917. 
Plate 23, figs. 11-14. 
1917. Membrendoecium pyriforme Canu and Bassler, Synopsis of American Early Tertiary 
Cheilostome Bryozoa, Bulletin 96, United States National Museum, p. 17, pi. 2, fig. 2. 
The zoarium incrusts bryozoa or small shells. The zooecia are very elongate, 
oval, distinct, and have a gymnocyst; the mural rim is prominent, smooth, some- 
what convex, enlarged on the margins, and much enlarged at the base. The 
opesium is oval, entire. The ovicell is endozooecial and is a small, smooth, distal 
convexity. The avicularia are very small, straight, salient, elliptical, often pro- 
vided with a gymnocyst. The ancestrula is surrounded by closed zooecia in which 
the frontal is perforated by an orbicular pore. 
. n • (Ac?=0.20-0.30 mm. 
Al ea-surements. — (Jpesia , 
r I lo= 0.13-0. 16 mm. 
„ . [Zs=0.40-0.50 mm. (Omitting the gymnocyst.) 
/moecia| fe==0 24 _ Q 3Q mm< 
Variations and affinities. — The length of the gymnocyst is quite variable even 
on the same zoarium; therefore in the micrometric measurements it is preferable not 
to count the gymnocyst, for many of the zooecia are devoid of it. The reduction 
of the zooecial length is frequent in this species and affects the entire zoarium : it 
is rather a rare occurrence when some mechanical obstacle is not opposed to the 
free development of the zooecia. 
This species is very closely related to Amphiblestrum, papillatum of Australasia, 
depending on Busk’s figures, which we reproduce on page 120. The micrometric 
measurements are identical. The avicularia appear a little larger and the ovicell is 
unknown. 
M embrendoecium pyriforme differs from M. rectum, in its much larger micro- 
metric measurements and in the presence of the gymnocyst. 
Occurrence. — Vicksburgian (Red Bluff clay) : 71 miles southwest from Bladen 
Springs, Alabama (very rare). 
Vicksburgian (Marianna limestone) : Murder Creek, east of Castlebury, 
Conecuh County, Alabama (very rare) ; Claiborne, Monroe County, Alabama (very 
rare) ; Salt Mountain, 5 miles south of Jackson, Alabama (common) ; deep well, 
Escambia County, Alabama (very rare). 
Lower Jacksonian (Moodvs marl) : Jackson, Mississippi ( very rare). 
Cotypes. — Cat. Nos. 63887, 63888, U.S.N.M. 
SECTION 3. OVICELL HYPERSTOMIAL, ALWAYS CLOSED BY THE OPERCULUM. 
It is not easy to recognize on a fossil form whether the opercular valve does 
or does not close the hyerstomial ovicell. After many dissections, which we have 
made on living species, we have recognized that generally ovicells of this kind leave 
a concave cicatrix above the mural rim, a part of which is thus concealed. There is 
evidently a great amount of uncertainty, but we can do nothing more with present 
knowledge. We would add that the different genera grouped in this section, 
