76 



PEOCEEDINGS OF THE NATIONAL MUSEUM 



In transverse section the tubes are polygonal, with adjacent walls. 

 The thickening of the walls of the mesopores forms a thick parietal 

 zone. 



In tangential section the mesopores are smaller than the tubes 

 because their orifice is inf undibuliform ; they are separated by a 

 thick, lamellose tissue. 



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Affinities. — This species differs from Leiosoecia grandipora, in which 

 the mesopores have the same dimension, in the smaller zoarium, in 

 the smaller aperture (not 0.12 mm.), and in the less regular ovicell. 



Occurrence. — Lower Cretaceous (Valangian) : Sainte-Croix, Switzer- 

 land (rare). 



Cotype.—Csit. No. 69930, U.S.N.M. 



