NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
433 
STOMACHETOSELLA CRASSICOLLIS Canu and Bassler, 1917. 
Plate 89, figs. 1-14. 
1917, Stomacheto sella crassicollis Canu and Bassler, Synopsis American Early Tertiary 
Clieilostome Bryozoa, Bulletin 96, United States National Museum, p. 45, pi. 4, fig. 7. 
Description . — The zoarium is free, bilamellar, formed of broad, undulated 
branching fronds, more or less flabelliform. The zooecia are elongated, little dis- 
tinct; the frontal is convex, smooth, thick and salient around the apertura and 
formed by a tremocyst with large tubules resting on a thin olocyst. The apertura 
(interior) is orbicular; the peristomice is provided with a triangular rimule-spira- 
men ; the false peristome is thick and smooth. The ovicell is hvperstomial, buried, 
globular, salient, ornamented with tubular tremopores; it opens into the peristomie; 
it is possibly closed by the operculum ( ? ) ; the rimule-spiramen of the ovicelled 
zooecia is longer and linear. Laterally, near the apertura there is often a triangular, 
improminent avicularium, the beak directed above, with pivot. 
Measurements— Peristomice J 7^6=0.10-0.15 mm. . j Lz=0.d() mm. 
(exterior) \lpe= 0.15-0.20 mm. °° ecia l/s= 0.30-0.40 mm. 
Apertura | Aa=0.12-0. 15 mm. 
(interior) 7 a= 0.12—0. 15 mm. 
Variations. — The variations are very important and apply to all the organs. The 
smooth peristome is altered in the old zooecia; it loses its anterior projection (figs. 
5, 6) ; it is not always salient (figs. 6, 7, 9). The tubules are rather constant in 
size (figs. 2, 3, 6, 9); they are obliterated, however, by the fossilization (fig. 8).' 
The zooecia are sometimes separated by a prominent thread (fig. 5). The walls are 
very thick (figs. 12, 13, 14) and there is a special one for each zooecium (fig. 14) ; all 
the walls are united among themselves but perfectly distinct; there are no walls 
in common. 
In the interior the apertures are orbicular; they appear elliptical and trans- 
versal in perspective because they are oblique. The wall is an olocyst with small 
perforations on which the tubules of the tremocyst are visible on account of its 
thinness. 
The tangential section (fig. 10) made at the level of the olocyst shows quite 
well the superposition of the two secretions. 
In vertical section it is easy to see that the passage of the ova is assured. 
It is not the same, however, for the evacuation of the. larvae. However the con- 
stancy of the forms of the peristomice and ovicelled zooecia seems to indicate that 
the operculum could always close the ovicell; but it is necessary to suppose some 
very long, special opercular muscles. 
This species with its enormous, solid walls, appears robust and resistant. 
Nevertheless this is not the case. It was rapidly exterminated and never had a 
large geographic distribution. This is frequent in the bryozoa where pliancy is 
a better sign of longevity and resistance. 
55899 — 19 — Bull. 106 2S 
