30 



There arc, therefore, six arms in eacli of tlie three rays preserved, in 

 our speeimeii. The ray on each side of the azygous area is injured, 

 but. we think, from a])pearanoes, we can safely call this a thirty 

 armed six'cies. After tlie arms become free tliey are composed of a 

 double series of inlcrlnrkin^ plates. 



Tlie first regular interradia! is very large and it is followed by 

 either one or two small plates which are cut off from all connection 

 with the vault by the union of the tertiary radials above. The azy- 

 gous plates cannot be drtcrinined in our specimen. 



The vault is coiucal but smaller than the calyx and bears a long, 

 central i)roboscis. which is broken off at the toj) of the specimen 

 illustrated. 



This is a marked species, and. if we were to guess at the age of 

 the rocks from which it canu", from an examination of the single 

 specimen, we would be inclined to say the Keokuk (xroup. But 

 some of the associated fossils fignred and described, in this Bulletin 

 and Bulletin No. 10. Iia\e the asl)(^ct of Burlington fossils. Some of 

 th(- (lovernmeid publications have called the rocks Carboniferous, 

 bid no sucii fossils were ever found in the Carboniferous rocks in 

 any jiart of the woi'ld. When we desci'ibed the forms in Bulletin No. 

 TO, we had no hi'sitation in saying they came from the Subcarboni- 

 ferous and we can now be certain that they are from the lower half 

 of the Subcarboniferous. Tt is ])robable that all the fo.ssils we have 

 examined are not, from the same layers and some may belong to the 

 Burlington anil others to the lower part of the Keokuk (J roup. 

 At preseid, we are inclined to refer them to the Upper Burlington or 

 Lower Keokuk, because none of tlieni are from rocks lower than the 

 Burlington or higher than the Keokuk, anil we do not know whether 

 they are or are not from rocks of the same geological age. 



Found by Karl Douglass, in whos(> honor we have proposed the 

 specilic name, on B>ridger .Mountains, near Bozeman. Montana, anil 

 now in the collection of S. .\. .Millei'. 



l)i)KVrKINrs sriK)Vll"(lKMIS. u. sp. 



I'liilr II. Fi(i. 7. ir.i/fiiiii^ side: Fiij. S. op/iofsitc lu'cir: Fii/. 0, sum- 

 in il ricir. 



Species medium size, calyx and vault together subovate. Calyx 

 nrri-shapeil, luirrowly rounded lielow. No radial ridges, but the 

 radial series project moderately at the arm bases, so as to notch the 

 circumforonco at the interradial spaces. Ambulacral openings 



