504 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



dorsal view, and the bottom part is wliollj or j^artly excavated. The calyx, 

 when placed in an upright position, rests either on the costals or distichals, 

 and leaves very little of the dorsal cup but the arm facets and second range 

 of interbrachials exposed in a side view. Plates of the dorsal cup flat, and 

 suture lines obscure ; those of the tegmen flat also, but their sutures are 

 somewhat depressed. 



Basals hidden from view, forming the bottom of the column concavity. 

 Eadials longer than wide, rapidly spreading. First costals rather large, 

 quadrangular, their upper faces wider than the lower; the second shorter, 

 twice as wide as long and pentangular. Distichals two in the calyx, very 

 short, especially the upper, which has a subcircular facet, and at the 

 ventral side is deeply notched by the ambulacral groove. Arm facets large, 

 and those of the same ray directed at right angles. Interradial spaces 

 somewhat contracted at the arm regions ; the first plate fully twice as 

 long as wide, and attenuate at the upper end ; the two of the second 

 range quite narrow, resting against the first distichals, and rising to a level 

 with the arm openings. First anal plate one third narrower than the 

 radials and slightly longer; the second anal narrow and long, narrower at 

 the lower end than at the upper; the plate at each side widest across the 

 middle. Ventral disk low hemispherical ; the posterior side slightly inflated, 

 but forming no ridge or lateral groove. Anus in close proximity to the pos- 

 terior oral, the opening turned obliquely upward. Posterior oral the only 

 plate of the tegmen whicli is convex ; the other orals and the radial dome 

 plates being not only flat but comparatively small ; the former somewhat 

 pointed at the outer end. 



Horizon and Locality. — Lower Burlington limestone ; Burlington, Iowa. 



Ti/pe in the University Museum at Ann Arbor. 



Remarks. — The depressed form of the ventral disk, the flatness of its 

 plates, the absence of any anal ridge, and the shortness of the costals and 

 distichals, are the most characteristic features of this species. 



A. decornis Rowley and Hare, and A. Blairi S. A. Miller, of which we 

 examined the types — the former in the collection of Mr. Rowley, the other 

 in that of Mr. F. A. Sampson — are identical with this species. The latter 

 was described from the Cliouteau group, but the color of the fossil and the 

 matrix seem to indicate that it came from the Lower Burlington limestone. 

 The subquadrangular outline of the calyx, to which Miller alludes as a spe- 

 cific distinction, is caused by the abnormal anterior ray of the specimen, in 



