THE NATURAL HISTORY SURVEY. 28 1 



length; the axis about two-sevenths of the entire width at the 

 anterior margin, limited laterally by strong lateral furrows, 

 tapering posteriorly to the base of the caudal spine, with eleven 

 or twelve annulations, the transverse furrows being deeply 

 impressed laterally, becoming broader and shallower and 

 arched forward over the median half of the axis; the pleura 

 moderately convex with a slight flattening upon the lateral 

 margins which can scarcely be designated as a marginal border, 

 marked by eight or nine strongly defined segments, all but the 

 posterior two or three of which are deeply grooved. 



The surface of the head, except in the furrows on the mar- 

 ginal and posterior borders and palpebral lobes, is covered with 

 rather coarse, scattered, rounded tubercles. The pygidium 

 is also tuberculate, each annulation o'f the axis bearing a strong 

 median tubercle with two or three upon each lateral slope; 

 upon the pleural segments each division bears a line of low 

 tubercles along its summit which are much less conspicuous 

 than those of the axis. 



The dimensions of an imperfect head are: width 37 mm., 

 approximate length along median line 22 mm., approximate 

 length to tips of genal spines 36 mm. The dimensions of an 

 imperfect pygidium are: approximate length 40 mm., width 

 46 mm. 



Remarks. This species has not been actually observed in 

 the Chicago area, but it occurs rarely in the dolomitic limestone 

 at Bonfield and elsewhere in Illinois, and may yet be found in 

 our area. Its tuberculate surface markings will, always serve 

 to distinguish it from other similar species of the genus. 



Localities Bonfield 111., and Jersey County, 111. 



