700 STUART WELLER 
ern Europe, which are lacking in a comparison of the New York 
and the European Silurian faunas. 
In the fauna of this age at Chicago and in northern Illinois, 
some remarkable forms of crinoids have been recognized which 
have not hitherto been recorded from America. One of these 
is Crotalocrinus, one of the most highly specialized genera of 
crinoids that has ever been described. Its arms, instead of being 
simply branched, as is usually the case, have the subdivisions 
joined laterally in such a manner as to form great, flat, flexible 
extensions from the body. It has been found most abundantly 
upon the island of Gotland, but it also occurs at Dudley, Eng- 
land, and is now found in the Chicago fauna. Two genera, 
Corymbocrinus and Pycnosaccus, founded upon Gotland specimens, 
are now found for the first time in America in the Chicago 
fauna. The first of these also occurs in England, but the second 
has been previously recognized only in Gotland. 
Petalocrinus is another highly specialized crinoid genus with 
the arm branches from each ray consolidated into a triangular 
plate or ‘“‘arm fan,” so that the creature with its arms extended 
closely resembles the corolla of a flower with five petals. This 
peculiar genus was first described by Weller* from Iowa, and 
later a specimen was found from Indiana. The genus is now 
known to occur in Gotland, and several species have been 
described from there by Bather.? 
Turning to the corals we find that the peculiar and highly 
specialized genus Gontophyllum, a quadrangular cup coral with 
an operculum of four triangular plates is found in England, Got- 
land and Jowa,3 but is recognized nowhere else. The peculiar 
little twisted brachiopod, Szvepizs, known both from England and 
the continent of Europe, has more recently been recorded from 
the Silurian near Batesville, Ark.4 
Now the presence of all these peculiar and highly special- 
ized forms in various localities in the Mississippi valley and in 
* Jour. GEOL., Vol. IV, p. 167. 
2(Quart. Jour. Geol. Soc. Lond., Vol. LIV, p. 4o1. 
3 Jour. GEOL., Vol. IV, p. 170. 
4 Am. Jour. Sci. (3), Vol. XLVIII, p. 329. 
