NEW CRINOID FAUNA 
289 
A NEW CRINOID FAUNA FROM MONTlCELLO, IOWA. 
A. 0. THOMAS. 
The purpose of this paper is two-fold: first, to bring briefiy 
before the members of the Academy the story of the discovery 
and a general description of an interesting but little known 
crinoid or sea-lily found some years ago near Monticello, and 
second, to call attention in a few words to some new inadunate 
crinoids recently collected by the writer in an outcrop of Si- 
lurian rocks at the same locality. 
The first-mentioned crinoid is the wonderful petal-crinoid, 
Petalocrinus mirahilis Weller, and is the most remarkable mem- 
ber of this new fauna. It was first collected near Monticello, 
Jones county, by Mrs. A. D. Davidson and was named and de- 
scribed by Professor Stuart WelleF of the University of Chi- 
cago. Two years later Dr. F. A. Bather^ of the British Museum, 
London, published a most exhaustive and excellent paper on the 
same crinoid and its relatives. 
Petalocrinus instead of having arms with free branches has 
all the divisions of each arm united into a solid fan-shaped piece. 
The calyx is depressed globular in shape and is about the size 
of a small slightly fiattened pea ; its plates are minute and firmly 
joined together. In life it was united below to a slender, jointed 
stem perhaps several inches in length and this was fastened 
by its lower end to the sea bottom. The five arm-fans, when 
attached, form a circle around the calyx at the same level near 
its top. On their upper or ventral surfaces the fans are ridged 
and grooved while their lower surfaces are smooth. Since the 
fans are curved dorsally or downwards instead of being flat a 
complete specimen may be likened somewhat to a tiny umbrella 
with the stem for its handle or perhaps to a small rose with 
five drooping petals. 
In the fossil state the arm-fans are usually detached and 
scattered and may be found highly silicified and adhering firmly 
to masses of fossiliferous chert scattered over the nearly drift- 
less, thin-soiled hills of the region. Mrs. Davidson and also Dr. 
iJour. GeoL, Vol. iv, ('1896) pp. 166-173. 
2Quart. Jour. Geol. Soc. London, Vol. 54 (1898), pp. 401-441. 
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