PLATYCRINID ZA. bar 
tapering only near the tips; the two lower arm plates suturally connected 
and quadrangular; the five or six succeeding ones wedge-form and uni- 
serial, those beyond interlocking, and gradually turning into two series of 
transverse pieces with parallel upper and lower faces. Pinnules heavy, 
| knife-like, the joints long and thickened at the ends. Ventral disk half the 
height of the dorsal cup, flattened at the summit, the sides steep, almost in 
a vertical line with the radials. The interambulacral spaces at the four regu- 
lar sides generally consist of six pieces, arranged in two rows; the middle 
one of the lower row large, the two at the sides very little curving, the three 
upper ones small. The interambulacrals of the anal side considerably wider, 
the middle plate of the first row shorter and descending to a lower level than 
the corresponding plates of the other sides, its lower faces making a right 
angle; the plates above numerous, forming a small protuberance, which 
opens out laterally, and is separated from the orals by several moderately 
large plates. 
florizon and Locality. — Lower Burlington limestone, Burlington, Iowa, 
and Hannibal and Sedalia, Mo. 
Type in the (Worthen) Illinois State collection, Springfield. 
femarks.— This species resembles P. burlingtonensis, but differs in the | 
more elongate form of the calyx; it has no such anal tube as that species, | 
its anus consisting of a simple opening directly through the disk. 
Miller’s P. carchesium, as described from the basals and radials only, can- 
not be separated from P. pilesformis. 
Platycrinus corbuliformis Rowtery and Hares. 
Plate LXXI. Figs. 11a, 0. 
1891. Kansas City Scientist, p. 113, Plate 8, Figs. 1 and 2. 
Of the type of P. burkngtonensis, but the plates heavier and more spread- 
ing. Described from specimens in which only the basals, radials and a few 
of the interradial plates are preserved. Dorsal cup basin-shaped, rather 
rapidly spreading, and distinctly quinquelobate at the upper end; the plates 
convex and perfectly smooth; interbasal, basi-radial and interradial suture 
lines rather deeply depressed. 
Basals forming a shallow cup, with a deep circular depression at the 
lower face for the reception of the column, which occupies about one third r 
the diameter of the cup; the lower margins a little bulging, and curving 
83 
