NORTH AMERICAN EARLY TERTIARY BRYOZOA. 

 ACCESSORY TUBES. 



641 



These are the zooecia closed or open which appear deprived of polypide. They 

 may occur on the dorsal (tergopores, firmatopores, nematopores) or on the frontal 

 (oactylethrae, cancelli). 



A B A 



FIG, 201. Diaphragms. 



A. Sketches showing aspect where a zooecium with a centrally perforated diaphragm is cut 

 longitudinally (B) and transversely (A) ; aa and 6&, intersection of the two longitudinal sections. 

 B. Sketches showing aspect where zooeciuni with a laterally perforated diaphragm is cut longi- 

 tudinally (B) and transversely (.4). C. Longitudinal thin section of Heteropora alvcolata 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 soine- 

 55899 20 Bull. 106 11 



