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PROCEEDINGS OF THE NATIONAL MUSEUM, 



smaller towards the center, or in the vicinity of the dorsal, which 

 indicates their widened nature (club shaped). 



The longitudinal sections are very difficult to make because of the 

 great thickness of the lamellar epitheca. The tubes are cylindrical 

 and are very long. There is no basal lamella, and although the 

 gemmation appears dorsal, because of the orientation of the tubes, 

 it is very irregular and occurs at all heights. A section reveals the 



A D 



Fig. 17. — A-D. Desmepora seruicylindrica Roemer, 1840. 



A. Meridian section, X 12, in a specimen with outspread pinnules. 



B. Transverse section, X 12, througli a pinnule and showing the cylindrical 

 tubes of the pinnule, the peripheral zone of lamellar tissue, the anterior zone 

 of polypidian tubes and the posterior zone of nematopores. 



C. Transverse section, X 12, not cutting a pinnule. 



D. Longitudinal section, X 12, through a branch with a very thick epitheca. 

 Cretaceous (Danlan) : Moen, Denmark. 



E-G. Desmepora rugosa D'Orbigny, 1854. 



E. Transverse section, X 12, through a pinnule and showing the three zones 

 of tubes as in Figure B. 



F. Longitudinal section, X 12, illustrating the zone of nematopores to the 

 left and that of polypidian tubes to the right. The vacuoles arise from the 

 nematopores. 



G. Longitudinal section, X 12, passing through the pinnules. 

 Cretaceous (Campanian) : Bonneville, France. 



presence of vacuoles, perfectly characterized by their curvature. 

 A second bears only nematopores with very thick walls; finally, 

 a third bears vacuoles below and nematopores above. These are 

 variations, in accordance with the general structure previously de- 

 scribed. 



The true arrangement of the tubes may only be known on the 

 meridian sections of the specimens with pinnules exactly parallel 



