(XVI.) 



ON THE CARBONIFEROUS XIPHOSUROUS FAUNA OF NORTH AMERICA. 



HEAD NOVEMBER IS, 1885. 



By a. S. Packard. 



By the kindness of Messrs. R. D. Lacoe, of Pittston, Pa., and .J. G. Carr, of jNIorris, 111., I 

 have been able to examine a most valuable collection of rare Xiphosuran fossils from Mazon 

 Creek, Grnndy 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, Cychis and Beliiuirus. 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 European strata. 



Of still more interest is the discovery of remnants of cephalic limbs in Cyclus 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 Cyelid(e, BelinurldcB, and Linmlidce, 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 Xijihosura and some strong resemblances to the Trilobites. 



Family CTCLID^ Packard. 

 Cyclus Americana Packard. PI. V, figs. 1, 1«, ; VI, figs. 4, 4a. 



Cyclm americana Pack., Anier. Naturalist, xix, 293, March, 18B5. 



In a nodule from Mazon Creek, Illinois, received from Mr. Lacoe, I recognize a species of this 

 rather obscure genus, vvhich 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 sejjaratedby aslight 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 



* Contributious to British fossil Crustacea. By Henry Woodw.ard, F. G. S.,etc. Geol. Mag.,vii, No. 12, pi. xxili, 



Dec, 1870. 



143 



