PLATYCRINIDE. 709 
depressed for the reception of the column. The interbasal suture lines 
indeterminable ; the basi-radial and interradial sutures. on a level with 
the plates. Radials rapidly spreading, considerably wider than long; the 
length of the lateral faces less than the width of the lower one; the limbs 
incurving, sloping outward and forming wide and deep notches between 
the plates; their upper ends sharply angular and higher than the upper part — 
of the facet. Facets large, occupying half the width and fully one third 
the length of the plates; deeply and broadly excavated at the upper end. 
Costals broadly triangular, rapidly sloping at the middle, their lateral exten- 
sions knife-like. First distichal placed obliquely, the second wider and 
higher than the first, and overlapping it laterally so as to touch the costals. 
Palmars of the same proportions as the distichals. Arms generally five to 
the ray, exceptionally six; cylindrical, very heavy and proportionally short. 
The ventral disk of this species was high, as indicated from fragmentary 
parts preserved in one of the specimens. The interambulacral regions appar- 
ently consisted of five plates, of which the middle one of the first row is very 
large, and nearly twice as wide as high, the two at the sides as long but 
narrower; the former having a central spine. Column distinctly elliptic, 
the edges of the joints studded with numerous small nodes. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa. 
Types in the collection of Wachsmuth and Springer. 
feemarks. — We were at first inclined to regard this form as a variety of 
P. Yandel ; but the differences in the size of the basal disk and the. propor- 
tions of the arms, as well as in the form of the dorsal cup, are so remarkable 
that we concluded eventually to treat it as a full species. It agrees in the 
form of the dorsal cup with the Discoideus group, but in the ornamentation 
and arm structure it is nearer P. Yandelli, P. verrucosus, and P. hemisphericus, 
and it doubtless represents a transition form. 
Platycrinus spinifer var. elongatus W. and Sp. (nov. var.). 
Plate LXVIT. Fig. 7. 
Very closely allied to P. spinifer ; the dorsal cup deeper, but very little 
expanding, the basal disk larger and almost flat. The radials rest upon the 
inner edges of the basals, and are as long as wide; their facets much wider 
than high, directed obliquely upwards; they extend to less than one third 
the length of the plates, but occupy half their width. Costals trigonal, 
