(XVL) 
ON THE CARBONIFEROUS ALTPHOSUROUS FAUNA OF NORTH AMERICA. 
READ NOVEMBER 18, 1885. 
By A. S. PACKARD. 
By the kindness of Messrs. R. D. Lacoe, of Pittston, Pa., and J. C. Carr, of Morris, Ill., I 
have been able to examine a most valuable collection of rare Xiphosuran fossils from Mazon 
Creek, Grundy County, Illinois, besides two specimens from the coal-beds of Pennsylvania. These 
_have revealed the existence on this continent of two genera, hitherto confined to the European coal- 
measures, viz, Cyclus and Belinurus. From the Pennsylvanian coal-measures a new species of 
Prestwichia has been obtained, and it is probable that ultimately we shall find as many species 
of this family as there are in Kuropean strata. 
Of still more interest is the discovery of remnants of cephalic limbs in Cyelus and Prestwichia, 
showing that in these animals the cephalic appendages were like those of the larval Limulus. It 
also appears that the ontogenetic development of Limulus is an epitome of that of the Xiphosura 
as a group. Furthermore, our studies have led us to restrict the Xiphosura to the three families 
of Cyclide, Belinuride, and Limulide, while certain upper Silurian forms referred by Woodward 
to the Eurypterida, and by Zittel placed among the Xiphosura, are, temporarily at least, referred to 
a new suborder, the Synziphosura, a group combining with features of its own, characteristics of 
the Xiphosura and some strong resemblances to the Trilobites. 
e 
Family CYCLID Packard. 
CYCLUS AMERICANA Packard. Pl. V, figs. 1, la; VI, figs. 4, 4a. 
Cyclus americana Pack., Amer. Naturalist, xix, 293, March, 1885. 
In a nodule from Mazon Creek, Illinois, received from Mr. Lacoe, I recognize a species of this 
rather obscure genus, which has not before occurred in North America, though in Europe nine 
species have been described. 
In form the animal is perfectly orbicular, the length being exactly equaled by the breadth, 
The body is regularly disk-shaped, flattened hemispherical, with the edge of the body broadly and 
regularly expanded, the margin being thin and flat, and apparently a little wider on the sides 
than on the anterior or posterior end. The inner edge of the rim is separated by an impressed 
line from the raised portions of the body-disk ; the surface of the rim is not plain and smooth, but 
ornamented by a series of plate-like, squarish markings, apparently separated by a slight impressed 
line, and with a slightly marked, raised tubercle on each plate or scale. 
There are no indications of segments either of the head or abdomen, nor are the limits between 
a head and abdominal region distinguishable, as is the case in Cyclus jonesianus Woodw.* There 
* Contributions to British fossil Crustacea. By Henry Woodward, F.G.S., etc. Geol. Mag., vii, No. 12, pl. xxiii, 
Dec., 1870. 
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