104 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



cause of these differences. The zoarium was probably attached to 

 algae by a slightly expanded base. The median lamella is salient at 

 the extremity of the frond. On the wide fronds of a certain thick- 

 ness the ovicell is partially covered over by the adjacent mesopores 



(fig- 7). 



In transverse section, the tubes are all equal (hence cylindrical) 

 even in the immediate vicinity of the median lamella (hence triparie- 

 tal gemmation) . The median lamella is rather thick . Our meridian 



Fig. 28. — Ditaxia parvipora, new species. 



A. Tangential section, X 16, sliowing few mesopores. 



B. Transverse section, X 16. 



C. Thin section cut obliquely through a zoarium, X 16, illustrating the struc- 

 ture in longitudinal section to the left, the basal lamella in the middle, the 

 median section above and below this, and the tangential section at the bottom. 



Cretaceous (Coniacian) : Tours (Indre-et-Loire), France. 



section cuts the branch just before a bifurcation in such a way that 

 a portion is transformed into a longitudinal section. The tubes ap- 

 pear clearly cylindrical, recurved at their extremity where the walls 

 are thickened; gemmation is triparietal. The mesopores are very 

 short and much expanded. On the meridian portion the tubes ap- 

 pear evidently lozenge-shaped. At the base of the section a portion 

 appears in tangential section caused by the undulation of the branch 

 due to ramification. 



