=. * 
ST Sn — —— ———~ = ———_—— = 
———— — —— 
= = = - 
ee ee a 
698 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
from the arm bases to the lower angles of the radials, where they meet with 
other ridges radiating from the column facet, with which together they form 
well defined rhombs. Similar ridges proceed horizontally from the radial 
facets to the sides of the plates, constituting a ring around the upper end of 
the cup. Hach rhomb encloses about twelve prominent, densely arranged 
nodes, and other nodes fill the triangular spaces between the rhombs. Basi- 
radial and interradial suture lines not grooved, the interbasal ones obsolete. 
Basal cup broadly obconical, its height equal to half the length of the 
radials; the column facet narrow. Radials slightly spreading, subquadrangu- 
lar, three fourths as long as wide ; the lower face equal to the lateral ones ; 
the limbs at the sides of the facets a little sloping, supporting a very large 
interradial plate; the facets extremely small, occupying less than one fourth 
the width of the plates, and entering but slightly the upper margins. Cos- 
tals pentangular, as long as wide, sharply angular at the top; the distichals 
as long, but a little narrower. Arms four to six to the ray, quite delicate, and 
composed of long, cuneate pieces which gradually interlock. The brachials, 
from the radials up, provided with well defined sharp projections at both the 
upper and lower ends; the middle portions deeply constricted, producing a 
somewhat zigzag appearance; the lines of union rather gaping. Pinnules 
moderately strong, and not in contact. The ventral disk is covered by the 
arms in the two specimens examined, with the exception of the interradials 
of the first row, the middle one of which is proportionally large and covered 
with nodes similar to those upon the radials, the two at the sides being nar- 
row and without ornamentation. Proximal stem joints circular, with small 
nodes surrounding their margins, 
Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa. 
Types in the Museum of Comparative Zodlogy. 
Platycrinus nodo-striatus W. and Sp. (nov. spec.). 
Plate LX VI. Figs. 5a,b6; Plate LXX. Figs. 3, La, b, c. 
Of medium size. Calyx globular, about as wide as high, rounded at both 
ends. Width of dorsal cup once and a half to twice its length, the entire 
surface of the plates densely covered with more or less confluent nodes, 
arranged in concentric lines around their margins, and traversed by two well 
defined ridges or rows of nodes passing out from the facets to the lower 
angles of the plates. The nodes surrounding the column facet more promi- 
ae," 
