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PLATYCRINID ZA. 689 
Type specimen in the American Museum of Natural History, New York. 
Ltemarks. — The Indian creek specimens sometimes have an additional 
row of ridges passing out to the sides, but otherwise agree with those from 
Burlington and Keokuk. Their arms also vary from four to six to the ray. 
Platycrinus canaliculatus Hatt. 
Plate LXXV. Figs. (a, 6. 
1858. Hat; Geol. Rep. Iowa, Vol. I., Part II., p. 539. 
1881. W. and Sp.; Revision, Part IT., p. 71 (Proceed. Acad. Nat. Sci. Phila., p. 245). 
re Se SS 
Calyx small, a little higher than wide, widest across the base of the 
radial facets; subovate, slightly truncated at the poles. Dorsal cup once | ih 
and a half as wide as high, the upper edge slightly inflected. Surface of 
plates marked by a few rather conspicuous nodes, of which generally twenty 
occupy the basal disk, two directed to each upper angle of the plate, while 
two others are parallel with the sides; the latter placed so close to the mar- 
gins as to give to the edges a serrated outline. The radials have three pairs 
| sia euesin. aie aeccaias nema os Goaaies: wavnesotbeaaa 
NTT EPR ENN ST 
of nodes passing downward, two of them running obliquely to the lower 
angles of the plates, the other pair vertically, following the median line. 
Two other nodes are placed close to the upper ends of the plates, one to : 
| each side. Basi-radial and interradial suture lines canaliculate, and the edges 
> of the plates beveled. | | | 
| Basals forming a flat disk, of which only the outer edges are seen in a i) 
side view ; the middle portion has a more or less deep rounded depression, ) 
wide enough to contain the top stem joint. Radials one fourth wider than i) 
’ long, very little spreading; the upper angles slightly truncated ; the facets . 
: semicircular, occupying nearly one third the width of the plates, thickened 
around the edges. Costals small, trigonal, their upper faces deeply notched. | il 
Ventral disk as high as the dorsal cup, distinctly stellate as seen from above. | 
Orals small, rather regularly arranged, forming an elevated area from which | 
the ambulacra pass outward and downward. Covering pieces strongly con- 1 
vex, and conspicuously elevated over the interambulacral spaces, which slope i 
abruptly from the orals at an angle of nearly sixty degrees, and form deep | 2 
trigonal depressions containing three plates each: a very large and nodose 
lower one, and two smaller plates above. The two plates at the sides of 
the larger one are narrow, and curve abruptly outward. Arms and column 
unknown. | (| 
87 
