NORTH A.MEUICAX EARLY TERTIARY BRYOZOA. 123 



MEMBRENDOECIUM PYRIFORME Canu and Bassler, 1917. 



Plate j::. tiirs. 11-14. 



1917. Membrciiiioccium ixjriftinin CAM: anil BASSLKB, Synopsis of American Karly Tertiary 

 Cheilostonie Hr.vox.ua. Bulletin !iti. 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 gymnoeyst; 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. 



. I Ao =0.20-0.30 mm. 

 Measurements. Opesia , 



1/0=0.13-0.16 mm. 



Zooeciaj, _ 



\Lz=QAO-Q.5Q mm. (Omitting the gymnocyst.) 

 ife=0.24-0.30 mm. 



Variation* aiuf 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 j><tj>/Ilntnm 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. 



Jfembrendoerium. pyrifo-nnf differs from M. rectum in its much larger micro- 

 metric measurements and in the presence oj: the gymnocyst. 



Occurrence. Vicksburgian (Red Bluff clay) : 7-i 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 (Moodys marl) : Jackson, Mississippi (very rare ) . 



Cotypes.Cat. Nos. 63887, 6388S, U.S.N.M. 



SECTION 3. OVICELL HYPERSTOMIAL, ALWAYS CLOSED BY THE OPERCULTJM. 



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 ovicell-; of thU 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. 



