PLATYCRINID^. 689 



Type specimen in the American Museum of Natural History, New York. 



Remarks. — The Indian creels; siDecimens sometimes have an additional 

 row of I'idges jjassing 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 Hall. 

 Plate LXXV. Figs. 7a, b. 



1S5S. Hall; Geol. Rep. Iowa, Vol. I., Part H., p. 539. 



1881. W. and Sp.; Eevision, Part II., p. 71 (Proceed. Acad. Nat. Sci. Phila., p. 245). 



Calyx small, a little higher than wide, widest across the base of the 

 radial facets ; subovate, slightly truncated at the jDoles. Dorsal cup once 

 and a half as wide as high, the upper edge slightly inflected. Surface of 

 plates marked by a few rather conspicuous nodes, of which general!}' 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 

 of nodes passing downward, two of them running obliquely to the lower 

 angles of the plate.s, 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 

 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 

 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. 

 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- 

 vex, and conspicuously elevated over the interambulacral spaces, which slope 

 abruptly from the orals at an angle of nearly sixty degrees, and form deep 

 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 



