NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
641 
ACCESSORY TUBES. 
These are the zooecia closed or open which appear deprived of polvpide. They 
may occur on the dorsal (tergopores, firmatopores, nematopores) or on the frontal 
( dactylethrae, cancell i ) . 
B 
A. Sketches showing aspect where a zooecium with a centrally perforated diaphragm is cut 
longitudinally ( B ) and transversely (A) ; aa and bb, intersection of the two longitudinal sections. 
B. Sketches showing aspect where zooecium with a laterally perforated diaphragm is cut longi- 
tudinally ( B ) and transversely ( A ). C. Longitudinal thin section of Heteropora alveolata new 
species, X 25, with more numerous diaphragms than usual in the genus. 
Tergopores . — The tergopores are ascending, transverse, accessory pores on 
the dorsal which are parallel to each other and as large as the polypidian tubes. 
They emanate from each other by successive bifurcations of their walls which are 
never adjacent; the new tergopores therefore always commence by the spreading of 
two neighboring walls. They are formed, first, of a longitudinal end portion sorne- 
55899— 20— Bull. 106 41 
