10) 004 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
ig Hh | dorsal view, and the bottom part is wholly or partly excavated. The calyx, | 
i when placed in an upright position, rests either on the costals or distichals, 
i, 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. 
Radials 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, 
iy. | | and those of the same ray directed at right angles. Interradial spaces 
mari; somewhat contracted at the arm regions; the first plate fully twice as | 
i long as wide, and attenuate at the upper end; the two of the second | 
ay | range quite narrow, resting against the first distichals, and rising to a level 7 
i fH with the arm openings. First anal plate one third narrower than the | 
: if al radials and slightly longer; the second anal narrow and long, narrower at | 
/ rad 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 | 9 
plate of the tegmen which 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. | 
Type in the University Museum at Ann Arbor. | | 
ftemarks. —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. Blaii 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 Chouteau 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 | 
