NORTH AMERICAN EARLY TERTIARY BRYOZOA. 433 



STOMACHETOSELLA CRASSICOLLIS Cann and Basslcr, 1917. 



Plate 89, figs. 1-11. 



1U17. Stomachetoaella cnifssifiiilia CANU and BASSLER, Synopsis American Early Tertiary 

 Claeilostome Brj-ozoa, 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 apei'tura and 

 formed by a tremocyst with large tubules resting on a thin olocyst. The a pert ura 

 (interior) is orbicular; the peristomice is provided with a triangular rimule-spira- 

 men; the false peristome is thick and smooth. The ovicell is hyperstomial, 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 f Ape=0.10-0.15mm. . fZs=0.90mm. 



(exterior) I fy<?=0.15-0.20 mm. ia l/.?=0.30-0.40mm. 



Apertura | Aa=0.12-0.15 mm. 

 (interior) I fa =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. 



5589919 Bull. 106 28 



