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frontal dorsal are aborted and engender the vacuoles of the non- 

 cellular face. 



Our longitudinal sections do not correspond exactly with those of 

 Gregory, 1899 (p. 364), which seem to show parietal mesopores 

 ( = maculae). The sections of Lonsdale are incomplete. 



The meridian section confirms the longitudinal section, but the 

 tubes are symmetrically arranged on each side of the central axis. 

 Moreover, diaphragms appear sometimes. 



In transverse sections the zoarial epitheca is thick, lamellar, per- 

 forated by irregularly scattered vacuoles; the tubes here are almost 

 equal and polygonal. 



Fig. 44.— Genus Siphodidyum Lonsdale, 1849. A-E. Siphodidyum hregulare, new species. A. Trans- 

 verse section, X 16, showing the polygonal tubes. B. Another transverse section, X 16, exhibiting the 

 central axis. C. Tangential section, X 16, illustrating the arrangement of the vacuoles around the 

 orifices D. Longitudinal section, X 16. The vacuoles perforate the epitheca all around the zoarium. 

 E. Longitudinal section, X 16, showing the cylindrical tubes and the vacuoles perforating the epitheca. 

 Lower Cretaceous (Aptian) : Faringdon, England. F-H. Siphodidyum gracile Lonsdale, 1879. F. Trans- 

 verse section, X 16. G. Meridian section, X 16. H. Longitudinal section, X 16, with the vacuoles 

 perforating the thick epitheca. Lower Cretaceous (Aptian): Faringdon, England 



In these various sections the zoarial pores appear, therefore, as the 

 extremities of small tubes perforating the zoarial epitheca; these are 

 vacuoles, as in the genus Eornera. Moreover, the general aspect of 

 the species is also that of Eornera, although the ovicell is decidedly 

 different, being that of the Ascosoeciidae. 



Affinities. — This species differs from Sipliodictyum irregulars in the 

 salient peristomes arranged in transverse rows and more numerous 

 on the cellular face; finally, branches formed entirely of vacuoles 

 have never been observed. 



Occurrence. — Lower Cretaceous (Aptian) : Faringdon, Folkestone, 

 etc., England. 



Plesiotypes.—C&t. No. 69943, U.S.N.M. 



