656 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
the middle one of the first row is subtriangular in outline, and as large as 
four or five of the others together. The middle plate of the anal side is 
somewhat smaller, and subquadrangular. It is followed by a very large num- 
ber of minute pieces, which form a circular, well defined, rounded protuber- 
| | ance, extending from the orals to the large quadrangular plate. In young 
i if specimens (Plate HI, Fig. 16), the orals are as large as in the adult (Plate 
‘| | LXIX., Fig. 1c); they are even more regularly arranged, and stand out con- 
spicuously over the surrounding part of the disk ; the ambulacra are shorter, 
and the interambulacral spaces consist of only five or six pieces, of which 
if | the middle one bears a central node. Column decidedly elliptic, except the 
Hh | proximal joints which are circular, and it has a rapid twist. The length of 
| | | : the stem, as observed in several specimens, does not exceed 15 cm.; its termi- 
Lys iE il nal part, after giving off a few short lateral cirri, ends in a sharp point. 
‘| Horizon and Locality. — Kinderhook group ; Le Grand, Marshall Co., Iowa, 
| Types in the collection of Wachsmuth and Springer. 
AY ian Remarks. — This species differs from P. Agassizi of the same horizon, in 
| | | | | the more spreading calyx, heavier plates, grooved suture lines, and the short 
and rounded basal cup without projecting rim. 
; 
|| | Platycrinus pileiformis Hatt. 
‘i i | | Plate LXIX. Fig. 5, and Plate LX X. Figs. 13a, b. 
| 1858. Hatt; Geol. Rep. Iowa, Vol. I., Part II., p. 529, Plate 8, Figs. 4a, 4, c. ' 
| 1881. W. and Sp.; Revision, Part II., p. 74 (Proceed. Acad. Nat. Sci. Phila, p. 248). f 
Syn. P. carchesium 8. A. Minter ; Geol. Surv. of Missouri, Bull. 4, p. 23, Plate 4, Figs. 6, 7. 
Of medium size. Dorsal cup deep, about as high as wide, somewhat 
i | _ expanding upwards, rounded at the base. Plates rather thin, except the 
i I | radials below the facets; surface smooth. ( 
| “ih h / | Basal cup basin-shaped, evenly rounded, its height fully half the length | 
a se of the radials, the middle portions slightly excavated for the column facet, 
3 ] ty which is circular; interbasal sutures rarely visible. Radials a little longer 
than wide, the sides almost parallel, the upper faces deeply notched, the 
| | notch of the anal side considerably wider and much deeper, giving to the 
| posterior radials an asymmetrical form. Facets semi-circular, less than half 
the width of the plates, their upper margins but slightly excavated. Costals 
triangular in outline, generally occupying the full width of the facets, those 
i of the same ray in sutural contact laterally, fully twice as wide as long, and 
i giving off two arms each. Arms four to the ray, very heavy, subcylindrical, 
