NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
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Phyllum MOLLUSCOIDEA. 
Class BRYOZOA. 
Subclass Entoprocta. 
The row of tentacles encloses both the oral and anal orifices. 
Subclass Ectoprocta. 
The tentacles surround the mouth only. 
Superorder PHYLACTOLAEMATA. 
Fresh-water Ectoprocta with the tentacles arranged in horse-shoe shape and 
the mouth protected by an overhanging lip. 
Superorder GYMNOLAEMATA. 
Almost exclusively marine Ectoproqfa with a circular row of tentacles surround- 
ing the mouth which is at their center. 
Order i. TREPOSTOMATA. 
Zooecia calcareous and superposed upon each other so as to form long tubes 
intersected by straight or curved partitions. Monticules or maculae of larger or 
smaller cells distributed on the surface at regular intervals. Range : Paleozoic only. 
Order 2. CRYPTOSTOMATA. 
Gymnolaemata differing from the Trepostomata in that the primitive part of 
the tube is usually much shorter and the passage to the mature region is more 
abrupt. Triparietal gemmation. Probably the Paleozoic representatives of the 
Cheilostomata. 
Order 3/ CTENOSTOMATA. 
Zooecia gelatinous or chitinous with tooth-like processes resembling a comb 
closing the aperture when the tentacles are retracted. Range : Paleozoic to Recent. 
Order 4. CYCLOSTOMATA. 
Zooecia calcareous and tubular with a circular aperture. Range: Paleozoic 
to Recent. 
Order 5. CHEILOSTOMATA. 
Zooecia calcareous or chitinous with the aperture closed when the polvpide is 
retracted, by a chitinous lip or operculum. Range : Mesozoic to Recent. 
STRUCTURE OF THE CHEILOSTOMATA. 
Bugula avicularia is here selected for description to illustrate the structure of 
the Cheilostomata, because it is one of the most common recent bryozoa found on 
the seashore in all parts of the world and is an example of the class frequently 
studied. It grows in brown or purple chitinous, bushy tufts several inches high, 
