LOWER CARBONIFEROUS FOSSILS. 515 



upon the primary septa, between which it is renewed at each interval. The 

 primary septa are more numerous here, and the peripheral portion, like the 

 floor of the calyce, is dense with stereoplasma; but within the second wall 

 they become suddenly extremely thin, sweeping in a strong- curve about 

 the rather large, solid columella. Dissepiments nearly absent. The sec- 

 ondary septa also have appeared, but bend abruptly to the left (looking 

 into the theca) and unite with the primary septa. The columella at this 

 point has become distinctly compound. 



Formation and locality: Madison limestone, limestone bluff north of 

 Little Sunlight Creek, Absaroka Range, 600 feet above the stream; White 

 Mountain, Absaroka Range; Arnold Hague. East side of Gallatin River, 

 west of Electric Peak; divide between Gallatin River and Panther Creek, 

 Gallatin Range; W. H. Weed. Crowfoot Ridge, Gallatin Range, bed 28; 

 J. P. Iddings and W. H. Weed. East slope of Survey Peak, Teton Range; 

 S. L. Penlield. Summit of Three River Peak. 



ECHIXODERMATA. 



PLATYCRINUS Miller, 1821. 

 Platycrinus symmetricus Wachsmuth and Springer. 



Platycrinus symmetricus Wachsmuth and Springer, 1890: Geol. Surv. Illinois, Vol. 

 VIII, p. 186, PI. XV, fig. 8. 



The material examined is unsatisfactory in that it has not permitted 

 the determination of the structure of the arms with absolute certainty, while 

 the character of the vault is completely hidden. The suture lines of the 

 five basals are quite invisible, forming an apparently solid and rather large 

 basal disk. The first radials, as in P. symmetricus, are slightly higher than 

 wide ; indeed, the whole calyx structure appears to be as Wachsmuth and 

 Springer have described it, except that the suture lines are not indented as 

 in the Iowa form, the whole surface being in the plane of curvature. The 

 absence of this character (the impressed suture lines) may be the result of 

 weathering. 



There are, apparently, thirty arms with the same structure as those of 

 P. symmetricus, but I can not assert this absolutely. 



P. haydeni Meek, described from Montana, 1 differs from the form in 



• Meek, 1873 : Ann. Rept. U. S. Geol. Surv. Terr, for 1*72, p. 469; White, 18*3: Ibid, for 1878, Pt. I, 

 p. 122, PI. XXXIII, fig. 7a. 



