PLATYCRINIDZ. gE 
Arms from six to seven to each main division, or twelve to fourteen to the 
ray; they stretch outward to the length of the palmars, and then bend 
upward and inward, being rounded on the back, flattened at the sides, and 
biserial from the second joint. 
Ventral disk fully twice as high as the dorsal cup, rather bulging; the 
plates large, heavy, and highly convex. Orals in contact laterally ; the 
posterior one central in position and larger than the others, which are oblong 
and pushed to the anterior side. The fixed covering plates of the ambulacra 
extend out from the orals beyond the limits of the calyx to about one half 
the length of the arms, and form together with the different orders of 
brachials large, tapering, tubular trunks, from which the arms are given 
off alternately at the sides. Interambulacral plates: 3, 2, 1, all large, but 
especially the middle one of the first row. At the anal side the middle plate 
is still larger, and is followed by nine or ten small plates, which take the 
place of the second row of plates at the other sides, and form a small pro- 
tuberance enclosing the anus. Above these plates there are two larger 
ones, which, together with the smaller orals, form a ring around the pos- 
terior one. Anal opening directed laterally. Stem elliptical, rapidly twist- 
ing, its long diameter nearly three times the shorter one; the joints slightly 
increasing in width, and their proximal and distal faces provided with a well 
defined ridge. 
Horizon and Locality. — Lower part of the Upper Burlington limestone, 
Burlington, Iowa, and several places in Missouri. 
Types in the collection of Wachsmuth and Springer. 
femarks. — This and the next species have the characters of the genus 
less pronounced than in the typical forms, and they represent transition 
forms in different degrees from Platycrinus. 
