LOWER CARBONIFEROUS FOSSILS. 513 



LITHOSTROTION Lhwyd, 1869. 



LlTHOSTROTION Sp. 



CorallTim compound, massive. Corallites small, about 7 mm. in 

 diameter, polygonal. There are usually in the neighborhood of thirty 

 radiating septa, alternately long and short. The longer ones extend almost 

 to the center. Transverse sections show that the whole interseptal space is 

 more or less vesicular. Toward the periphery the vesicular tissue is coarse, 

 stretching in extended loops, among which, in some individuals, the periph- 

 eral ends of the septa lose themselves. In others the septa can be traced 

 quite to the inclosing wall. Toward the center the vesicular appears to 

 o-ive place to dissepimental tissue, and regularly a series of these dissepi- 

 ments equally distant from the center are thickened and joined together to 

 form a sort of inner wall. This inner wall is circular in section, having a 

 diameter of about 4 mm. The septa, too, appear thicker and denser at this 

 point, so that the demarcation between the inner and outer zones is well 

 marked. In the inner zone is found localized dissepimental tissue, which 

 usually unites to form one or two concentric sheaths about the columella. 

 The latter is linear, often united at either end with two opposite septa which 

 bisect the corallite and give it a conspicuous bilateral symmetry. The 

 other primary septa terminate in one of the columella sheaths, as do often 

 all the primary septa. 



The calyces are deep, flaring toward their mouth. The columella 

 projects from the center of each, high, thin, and knifelike above, but below 

 thicker and complicated with ridges. About thirty alternating septa are 

 present, of which the primary ones descend into the calyce and unite with 

 the columella at its thicker complicated base. 



Longitudinal sections where not central show an outer vesicular zone, 

 the strong vesicle walls curving downward and overlapping, thus forming 

 by their inner surface the so-called inner wall of the theca. Within this 

 are the vertical, parallel, cut edges of the septa intersected by dissepiments, 

 or what appear sometimes to be upward-arching tabulae. In a section 

 through the columella the septa are not seen, only the upcurving tabulae, 

 cut by the linear columella. 



Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin 



MON XXXII, PT II 33 



