204 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



ambulacral plate is somewhat wider, and perforated by the anus to such an 

 extent as to leave only a narrow skeleton at the lateral margins. 



Gazacrinus Miller is identical with Idiocrinus, the latter name having 

 priority. Miller described the genus as monocyclic instead of dicyclicj and 

 he speaks of a " vault sustained by a specialized frame work with ambulacral 

 canals connecting the arms with the central orifice." This is misleading, for 

 the plates exposed at the oral surface are true plates of the disk, and the 

 open spaces whicb appear in the specimen>s were closed by orals and ambu- 

 lacral plates. There was no central orifice, the peristome being covered as 

 in all other Camerata. 



Horizon and Locality. — Upper part of Niagara group ; St. Paul, Shelby 

 Co., Ind. 



Tyjpe in the collection of Wachsmuth and Springer. 



Remarks. — Mr. Miller, in describing the arm plates of this species, 

 states they are long, and their edges " are transversely serrated on the 

 inside, half the depth of the plates." We observed this structure in our 

 specimen, and were at first inclined to regard the edges as formed of small 

 side pieces, and so described them in the " American Geologist." Since then 

 on further cleaning the specimen, we have become convinced that the parts 

 in question are mere extensions of the arm plates, which are short, and that 

 the line of union is slightly gaping to facilitate motion. 



Another point in Miller's description should be noticed. He says : "There 

 are three longitudinal furrows on the inside of each radial series, shown at 

 the top of the secondary radials ; this gives fifteen ifurrows at the top of the 

 secondary radials, one in the middle of each plate, and the other at the 

 suture ; " and he alludes to this as a peculiarity entirely new to him. He 

 evidently misunderstood the structure, for our specimen clearly shows but 

 one furrow to each brachial, of which those from the distichals unite upon 

 the axillary costals at the extreme edge of the disk. The supposed marginal 

 furrows do not enter the disk, and are mere depressions at the lateral margins 

 of the distichals, formed by the highly projecting serrated edges of the 

 ambulacral furrows at each side. 



