514 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Range, bed 28 ; J. P. Iddings and W. H. Weed. Head of Gallatin River, 

 west of Three River Peak; Arnold Hague. 



CLISIOPHYLLUM Dana, 1846. 



Clisiophyllum teres n. sp. 



PL LXVII, figs. 2a, 26, 2c, 2d. 



Corallum of medium size, tapering, slightly curved, and often laterally 

 compressed; but little marked by constrictions and irregularities of growth. 

 Length from 75 to 100 mm.; diameter of about 25 mm. There are fifty- 

 three septa of the first order; secondary septa short and coalescing with 

 the primary ones. Columella small, complex, composed of radiating and 

 concentric plates. The primary septa extend to the center and are there 

 connected with the columella, about which they twist. Dissepimental tissue 

 present in moderate abundance. Fossula well marked, situated on the 

 convex side, bisected by the fossular septum. 



This description is not taken from any one specimen, but is the result of 

 observations made on somewhat fragmentary material from several localities. 



The specimen figured is a somewhat undersized individual, from the 

 summit of Three River Peak, referred to this species. A section taken 

 where the diameter is only 7.5 mm. shows thirty-two (primary) septa, 

 which are thick and straight, joining tlie columella, like radii drawn from 

 the center of a circle, and not twisting around it, as they do later. The 

 columella is large, apparently solid, showing a diametric line of greater 

 density in the direction of the fossular septum. Fossula large. Dissepi- 

 ments numerous and rather regularly disposed, but not enough to suggest 

 tabula?, which appear to be absent. No secondary septa have yet made 

 their appearance. 



A section taken near the distal extremity, where the diameter is about 

 14 mm., shows a different condition. It appears to intersect a basin- 

 shaped tabula, or perhaps the floor of the calyce, for we see the appearance 

 of a strong inner wall, which is evidently traversed obliquely by the plane 

 of the section. It is decidedly eccentric, being only about 2.5 mm. from 

 the periphery at the fossula and twice as far at the opposite diameter. 

 This tabula is apparently dissepimental in its nature, and not an inner wall, 

 because it does not begin at the bottom of the theca, because it is seen in 

 section to be strongly divergent, and because it depends for its expression 



