NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
555 
The mode of calcification of the Adeonidae is more complicated. The primi 
tive olocyst secreted by the endocyst is rather thin. It is covered by a pleurocyst 
secreted by the endocystal elements which pass through the parietal areolae and 
deposit over all of them more or less considerable quantities of lime. When the 
deposit is somewhat thick the parietal areolae are transformed into true tubules 
(pi. 15, fig. 14, and text fig. 163H). In transverse thin sections the pleurocystal 
elements superimposed and oriented in radial fibers (pi. 99, fig. 16) can be clearly 
seen. 
The frontal avicularium is never visible in the interior; it early has no com- 
munication with the zooecia, and it is therefore nourished exteriorly by the endocyst 
proceeding from the areolae and covering the skeleton. 
In tangential thin section these pleurocystal elements are very irregular and 
are grouped in still more irregular fila- 
ments (pi. 15, fig. 15). This is the 
characteristic of this secretion, which is 
very rare in the Anasca, but which de- 
velops frequently in the other Asco- 
phora, and attains its maximum of de- 
velopment in the Adeonidae. 
Classification. — The essential char- 
acters of classification of the Adeonidae 
have been given by Waters and Levin- 
sen. There are three principal groups. 
The first comprises the species which 
are without frontal ascopores. This is 
the family Meniscoporidae Canu, 1907, 
composed of Smittistoma , Meniscopora , 
Schizostoma , Calvetina , and Brace- 
Hridgia. The second group is composed 
of the species which are provided with 
a spiramen and contains the single genus Adeonella. The third group contains 
the species which are provided with frontal ascopores and embraces the genus 
Adeona if the ascopore is simple and the genus Adeonellopsis if the ascopore is 
stellate. 
Genus MENISCOPORA Gregory, 1893. 
1893. Meniscopora Gregory, British Palaeogene Bryozoa, Transactions Zoological Society, 
London, vol. 13, p. 250. 
The zooecia are trimorphic. The normal axial zooecia have an external aper- 
ture straighter than that of the marginal zooecia ; the aperture is formed of a 
semilunar anterior and of a very concave posterior part. The gonoecia are larger 
than the ordinary zooecia and their aperture is of different form. The peristomie 
is of slight depth. Interzooecial avicularia are rare. Certain lateral areolae are 
transformed into small frontal avicularia. 
A *55 
Fig-. 165. — Genus Meniscopora Gregory, 1893. 
A. Meniscopora bigibbera Gregory, 1893. Zooe- 
cia, X 55. (After Gregory, 1893.) 
B. Meniscopora simehi Canu, 1907. Views of per- 
istomice and apertura, X 80. (After Canu, 1907.) 
ae, peristomice of zooecium; ai, apertura of a zooe- 
cium; ge, peristomice of agonoecium; gi, apertura 
of a gonoecium. 
