CARBONIFEROUS MYRIAPODA OF ILLINOIS. 439 



as high and is traversed longitudinally by fine lines breaking it up into frustra of ex- 

 ceeding slenderness, perhajjs eight or ten tinies longer than broad. The legs are ex- 

 ceedingly slender, finely tapering to a delicate point, and about as long as the width 

 of the body. 



Length if extended, 44 mm.; breadth, 2.25 mm. 



The species is mainly peculiar for the exceedingly narrow frustra, but also for the 

 altei-nation of longer and shorter segments which appears wherever two adjoining seg- 

 ments are clearly defined. It Ijears certain resemblances to the interesting Kampecaris 

 forfarensis Page, so carefnlly described and figured by Mr. Peach of the Geological 

 Survey of Scotland; more indeed than to any myriapod yet described from this con- 

 tinent. But the smaller segments are much less important than there, the feet are much 

 slenderer and Mr. Peach makes no mention whatever of anything akin to frustra. Our 

 own species is represented by specimens far less perfect than his and does not admit of 

 a really satisfactory comparison. 



Xylobius mazonus. 

 PI. 37, figs. 7-11. 

 X>jlohius mazonus SciuU., Zittel, Ilandb. d. Palaeont., i, ii, 730, fig. 902b (1885). 



The first specimen of this species which came under my notice was received from Mr. 

 Lacoe with the number 1809ab, and was intei-esting from being the first myriapod 

 seen from Mazon Creek in which the segments were broken into frustra, and much 

 larger than other species of the genus, found heretofore only in the sigillarian stumps 

 of Nova Scotia. This specimen (fig. 7) is preserved on a side view, and shows a gently 

 arched body, bent a little behind the head; excepting near the extremities, which taper 

 considerably for half a dozen segments (fig. 9), the body is of nearly uniform width; it 

 is complete, and composed of numerous very short segments, obscure in places but ap- 

 parently numbering about fifty. The form of the body and its general appearance at 

 first recall the commoner Euphoberiae of these beds, but a closer examination soon 

 shows considerable differences. Spines are wanting, the extremely shoi-t and broad 

 segments extend the whole width of the body and are broken regularly into frustra; the 

 legs are very delicate and not very long, and the head is not lai-ger than the segment 

 behind it. The segments are about six times as broad as long and the frustra unusually 

 narrow, being fully four times as long (equal to the width of the segment) as broad, as 

 shown in the enlarged sketch (fig. 8) of two or three adjoining segments a little in 

 front of the middle of the body. The legs are very slender, and apparently cylindrical, 

 but their full length shows only at the hinder extremity of the body where they equal 

 its diminished diameter. The specimen is 61 mm. long; 5.5 mm. broad in the middle; 

 2.75 mm. broad at the head end; the longest legs at the posterior end are about 4 mm. 

 long. 



The second specimen (figs. 10-11) is more interesting on account of its perfection. 

 It was also received from Mr. Lacoe and bears the number 1809cd, in his collection. 

 It also shows a side view, gently arched, especially toward the head end, which is appar- 

 ently complete though obscure, while the hinder end is partly concealed under stone, 



