PETALOCRINUS MIRABILIS 167 
‘environment than are the crinoids. Because of this it is not sur- 
prising that during a change or migration which did not even 
bring about a modification of the specific characters of the coral 
Goniophyllum, the generic and even family characters of the cri- 
noid became modified. The peculiar family of Crotalocrinide has 
heretofore stood out alone among all the crinoids, and now a 
new family is discovered in America which is just as peculiar 
and whose bonds of relationship are strongest with the European 
Crotalocrinus. 
Only a few of the most remarkable species of the fauna are 
described in the present paper. Corals are exceedingly abun- 
dant in the fauna, in fact it seems probable that these Iowa beds 
are the remnants of an ancient coral reef where many species of 
these animals flourished. It is hoped in the near future to make 
an exhaustive study of the whole fauna and its relationships. 
PETALOCRINIDE (n. fam.). 
No special description of the family will be attempted, all 
the characters, family, generic and specific, will be recorded 
under the description of the species. 
PETALOCRINUS MIRABILIS (x. gen. et sp.). 
Plate VI., Figs. 2-5. 
The entire crinoid resembles a flower with five petals fully 
expanded, the five leaf-like arms representing the petals. The 
diameters of the calyces of the two perfect specimens in the 
collection with all the arms intact, are respectively 3, and 4% 
inch, the total expanse of the arms being 7g and 1% inches. 
Some of the detached arms indicate individuals whose total 
expanse of arms was nearly two inches. 
Calyx monocyclic, depressed. Basal plates 5, rhomboidal. 
In four of them the two outer edges are a little shorter than the 
inner; on the anal side the two outer edges are about equal 
to the inner. First radials resembling those in /Vatycrinus, 
a little wider than long, extending nearly horizontally from the 
basal plates. Second radials very short, free, as in Platycrinus, 
bearing the arms. They appear as thin plates intercalated 
