8 LINDSTRÖM, ON THECOCYATHUS NATHORSTI. 



The same sort of papillas are also seen in the septa of the 

 third cycle (fig, 4), even of larger size than in any of the both 

 first cycles. 



A quite different aspect of the arrangement and structure of 

 the septa is gained through horizontal sections below the cali- 

 cular surface. 



Tliere we find that peculiar arrangement of the septa in 

 bundles, which is so common not only in other species of this 

 genus but also in other Turbinolian genera as Deltocyathus, 

 Leptocyathus and others. The septa of the third cycle converge 

 towards those of the second and first cycles and join them at 

 their inner edge. This is well shown in the sections above 

 (figs 6 — 8). In figure 7 no less than six such alliances are 

 perceptible. In the oldest section (fig. 5) they are obliterated 

 through the incrassation of the septa. It is a peculiarity which 

 disappears during continued growtli and there is no trace of it 

 in the latest stage of the calicle. 



In the same sections the septa have been solidified and no 

 papillär exist there, the septa continue without Interruption to 

 the central axis, which is a homogenous cylinder, no doubt formed 

 by the union of the inner septal edges. And the deeper down 

 a section is taken, the more incrassated the septa have become 

 till at last in a section near the basis the loculi are almost 

 obliterated, being narrow slits, thus approaching the ultimate 

 stage, where there is no more distinction between septa and 

 loculi and the whole is a solid, homogenous mäss. 



The lateral surfaces of the septa are covered with small 

 wartlets. These have grown long and formed into small spines 

 which Stretch across a loculum (fig. 7 — 8) from one septum to the 

 opposite one or coalescing with the spines from the other side thus 

 forming a complicated network in the locula, which becomes more 

 intricate through their branching and uniting and also going parallel 

 alongside with the septa. These spines in a certain way have 

 the appearance of a sort of a falsa dissepiment, being, however, 

 greatly different from the true one which consisting of convex 



