({IS PALEONTOLOGY OF ILLINOIS. 



narrower anteriorly; segments of mesial lobe seventeen or 

 eighteen, well defined, rounded, and very nearly or quite 

 straight. Lateral lobes more depressed, and about one- 

 third or one-fourth wider than the mesial lobe, rounding 

 down rather abruptly to the lateral margins ; segments nine 

 or ten, rounded, simple, and separated by distinct furrows ; 

 all terminating abruptly at the inner edge of the broad, 

 smooth marginal zone. 



Entire surface apparently very nearly smooth. 



Length of cephalic shield, exclusive of posterior lateral 

 spines, 0.45 inch, breadth of same, 0.66 inch, hight of do., 

 0.31 inch. Length of glabella, exclusive of the neck seg- 

 ment and anterior border, 0.36 inch ; breadth of same across 

 the posterior lateral lobes, 0.29 inch ; do. of same across 

 the constricted central region, 0.25 inch; do. of same ante- 

 riorly, 0.28 inch. Length of eyes, 0.18 inch. Length of 

 pygidium, 0.50 inch ; breadth of do., 0.55 inch. 



Locality and position Springfield, Illinois. Upper Coal Measures. 



Genus DITHYROCRARIS, Scouler. 



\ 



DlTHYROCARIS CARBON ABIUS, M. and W. 



PI. 32, Fig. 1. 

 IXthyrocaris carbonarius, MBEK and WORTHEX, 1869. Proceed. Acad. Nat. Sei., Phila. 



WE only know this fossil from a specimen showing the 

 caudal appendages that is, the telson* and stylets. These 

 are lanceolate in general outline, and rather flattened. 

 The telson seems to be a little shorter than the stylets, and 

 more rapidly tapering toward the extremity. Below, it is 

 flattened, and has a faint, undefined, obtuse, longitudinal 

 ridge along the middle, with on each side an equally unde- 

 fined, shallow sulcus between this and the lateral margins, 



* If the middle one of the three nearly equal caudal appendages in this genus is not articulated at 

 its base, it would only be, properly, an attenuated terminal part of the telsoii, and not the whole of that 

 appendage. 



