NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
209 
Affinities and variations. — In reality the zooecia are not dimorphous, for their 
micrometric dimensions are very similar; but there are actually two kinds of 
opesia. One is large, elongated, elliptical, with neither polypidian convexity, nor 
opesiular indentations; the other is small, transverse, with polypidian convexity and 
opesiular indentations (zooecia a). These two kinds of zooecia occur without 
apparent order, and we are in ignorance regarding the use of the large opesia. 
Occurrence. — Middle Jacksonian: Wilmington, North Carolina (very rare); 
Rich Hill, Crawford County, Georgia (common) ; Eutaw Springs, South Carolina 
(common). 
Upper Jacksonian (Ocala limestone) : Along the west bank of Sepulga River, 
Escambia County, Alabama (very rare). 
Cotypes. — Cat. Nos. 63961-63963, U.S.N.M. 
Fig 57. — Genus Rectonyclwcella Canu and Bassler, 1917. 
A-E. Rectonyclwcella solida Nordgaard, 1907. A. Zooecia and onychocellarium, X 24. 
B. Longitudinal section of a zooecium, X 36. bv, basal wall ; dp, distal dietella ; dv, transversal 
wall ; fv, frontal wall ; Ip, lateral septulae. C. Sketch showing mandible in place, X 24. k, lunate 
chitinous mass; me, corneous membrane; onw, passage of occlusor muscles; r, rachis. D. Ele- 
vator muscles of the mandible, X 70. E. Opercular valve, X 50. (A-E after Norgaard, 1907.) 
ect, ectocyst ; op, opercular valve ; scl, sclerite. 
Genus RECTONYCHOCELLA Canu and Bassler, 1917. 
1917. Rectonyclwcella Canu and Bassler, Synopsis of American Early Tertiary Cheilostome 
Bryozoa, Bulletin 96, United States National Museum, p. 25. 
The retractor muscles of the polypide are attached in the median axis of the 
zooecia. The opesiular indentations are symmetrical. The onychocellaria are 
straight, and their opesium presents a posterior part, narrow and denticulated; 
the mandible is composed of two membranes. The zooecium is closed by an 
opercular valve. The mural rim is not separated from the crvptocyst. 
Genotype. — Onychocedla solida Nordgaard, 1907. 
Range. — Jacksonian — Recent. 
55899— 19— Bull. 106 14 
