108 CAKBONIFEROUS PERIOD. 



hiserialis is now Ivnown to extend over an area more than one thousand 

 miles across in a dii-ect line, throughout the whole extent of which it is sm-- 

 prisingly constant in its specific characters, and just as constantly different 

 from those of 8. virgidacea as that species is represented by the figures and 

 descriptions of European authors. The European species is without the 

 mesial carina of ours, but has in its place a median row of pores, which our 

 species never has. 



Position and locality.-^— '^ixix.ia of the Carboniferous period (Red Wall 

 limestone) ; Camp Apache, Maricopa County, Arizona. 



Genus POLYPORA McCoy, 1844. 



Polypora stragula White. 



Plato VII, fig. 4 a and i. 



Polypora hiarmica Geinitz, 1866, Carbonformat. unci Dyas in Nebraska, 68 (uot P. 



Marmica Keyserling). 

 Polypora (species uiuleterraiued) Meek, 1872, U. S. Geol. Surv. Nebraska, 155. 

 Polypora stragula White, 1874, Exp. & Surv. west lOOtli Meriil., Prelim. Rep. Invert. 



Eoss., 19. 



Polyzoary apparently flabelliform ; longitudinal branches bifurcating 

 with more or less in-egularity in difi'erent parts of the polyzoary ; dissepi- 

 ments little if any more than half as wide as the branches ; fenestrules oval 

 or oblong, the porportions of length and width varying in different parts of 

 the polyzoary from about one-quarter longer than wide to twice as long as 

 wide; varying also in size in different parts of the polyzoary, but averaging 

 about six in number within the length of a centimetei*, measured longitudi- 

 nally ; poriferous side of branches furnished with from four to six indistinct 

 rows of small thick-set pores of uniform size, the aiTangement of them in rows 

 being more distinct obliquely than vertically; dissepiments usually free 

 from pores, except near their junction with the branches, and a slightly- 

 raised median ridge is often seen upon them. 



This species is known to occur in the Carboniferous rocks of Iowa, 

 Missouri, and Nebraska. It was from the latter State that Dr. Geinitz 

 obtained the specimens which he refen-ed (loc. cit.) to P. hiarmica Keyserling, 

 the type-specimens of which species were obtained from Permian strata of 

 Petschoraland. Mr. Meek {loc. cit.) has pointed out very clearly the differ- 



