ZAPHREXTOIDEA. 



29/ 



ment of the septa, Paltzocyclus porpita differs from the group of which 

 Had?'ophyUum is the type. The affinities of Palceocyclus cannot be 

 regarded as clearly established. It is possible that the genus, instead 

 of being placed here, should be looked upon as holding the same 



Fig. 177. — Palceocyclus porpita, from the Wenlock Limestone of Gotland, a. Upper surface 

 (calice) of the corallum, showing the cardinal septum in the fossula {h) ; b, Side-view of the 

 corallum ; c. View of the flat under side of the corallum, with the concentrically striated 

 epitheca. All the figures are enlarged about twice. (Original.) 



position to the Heliophy Hides that Hadrophyllum and its allies do to 

 the Zaplwentidce. 



The genus Strepielasma may be regarded as the type of another group 

 of Zaphrentoid Corals, to which the name Streptelasmidce may be given. 

 The corallum in this genus is simple and turbinate or conical in form. 

 A true " theca " does not seem to be present, but the septa become much 





w/Mmm 



#!<;> ,■■■ ■ ■■^■■■Jw 



Fig. 178.— Structure of Strepielasma corniculum, from the Ordovician rocks (Cincinnati 

 Group) of North America, a. Transverse section; b, Longitudinal section of the corallum. 

 enlarged twice. The transverse section shows the thick false wall formed by the fusion of the 

 outer portions of the septa, h, Cardinal septum situated in the fossula ; g, Counter septum. 

 In the specimen figured there are one hundred and eight septa, alternately long and short. 

 (Original.) 



thickened towards their outer edges, being fused with one another by 

 their lateral margins for a considerable distance, and thus giving rise to a 

 dense false wall (figs. 127, B and 178, A). The septa are numerous, of two 

 orders, alternately long and short, the latter being buried for the greater 

 portion of their length in the false wall. The symmetry is distinctly bi- 



