512 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. 



fossula is bisected by a cardinal septum, which also reaches to the middle 

 and is there connected with the other septa. The theca and all the septa, 

 except the cardinal septa, are sometimes so thickened by stereoplasmic 

 deposits as to form a nearly solid mass, obscuring details of arrangement. 

 This description is taken from a section below the calyce, well down in the 

 septate portion. 



A section through another coral, apparently at a somewhat later stage 

 than the above, shows a very interesting condition. The septa on one side 

 of the theca, about fifteen in number, are inclined toward a point, eccentric, 

 and lying within the diametral segment under discussion. Their ends are 

 bent and connected by a thick stereoplasmic deposit into a counterseptal 

 wall. There are twelve other septa. Of these, six on one side and five on 

 the other are inclined toward the visceral wall aforesaid, and their bent 

 ends are united into a partition which, in one case, appears to connect with 

 the counterseptal wall, and in the other is still free. This leaves a wide 

 terminally inflated fossula, but the septum occupying it, or cardinal septum, 

 is very short. There is no stereoplasmic thickening. 



Another section through the same specimen, at a point farther from 

 the apex, shows the primary septa (twenty-nine in number) inclined 

 and with bent terminations as before described, but not extended so as to 

 form by their ends three visceral partitions — a counterseptal and two alar. 

 The secondary septa are represented by low ridges. The fossula is strongly 

 marked. It is partly distinguished by the nondevelopment of the fossular 

 septum, which is scarcely more strong than the two secondary septa 

 between which it stands; and all the septa diminish in size as they approach 

 the cardinal septum. 



Another section, farther toward, yet still some distance from, the mouth 

 of the calyce, shows thirty short primary septa with as many still shorter 

 secondary septa. The general position alone of the fossula is indicated by 

 the obsolescence of the septa in that region. 



Formation and locality: Madison limestone, near summit of ridge, 

 west end of Hunter Peak, Absaroka Range; Upper Gallatin Valley west 

 of Bighorn Pass; Arnold Hague. Crowfoot Ridge, Gallatin Range, bed 

 25, lower part of bed 27, bed 31 ; J. P. Iddings and W. H. Weed. South 

 of Forellen Peak, Teton Range ; S. L. Penfield. South base of Quadrant 

 Mountain, Gallatin Range ; J. P. Iddings. Crowfoot Ridge, Gallatin 

 Range, cherty limestone, top of bed 24 ; A. C. Gill. 



