THE NATURAL HISTORY SURVEY. 253 



of the head, which is entirely smooth or is marked only with 

 a small central tubercle, no median spine ever being present. 

 The lateral lobes of the glabella are always distinct. 



Odontopleura illinoiensis, n. sp., pi. xxm, figs. 5-6. 



Description. Cranidium sub-quadrangular exclusive of 

 the posterior portions of the fixed cheeks which are produced 

 laterally. Glabella sub-cordate in outline, prominent, the 

 lateral lobes but slightly depressed below the median lobe, a 

 little wider than long, the greatest width at the middle of the 

 posterior lateral lobes. Dorsal furrows well-defined, becom- 

 ing deeper posteriorly where they join the occipital furrow. 

 Median lobe of the glabella elongate, sub-quadrangular in out- 

 line, broadest in front, extending to the occipital furrow. An- 

 terior lateral lobes obsolete; second lateral lobes strongly con- 

 vex, sub-ovate in outline; posterior lateral lobes more than 

 twice as large as the second pair, strongly convex, sub-elliptical 

 in outline, their longer axes directed antero-laterally. Anterior 

 glabellar furrows obsolete; second pair deeply impressed at 

 their antero-lateral extremities, shallower within, curving 

 posteriorly and joining the third pair of furrows; third pair 

 of furrows more deeply impressed in their anterior half than 

 the second, shallower behind where they curve posteriorly and 

 join the occipital furrows as shallow rounded furrows. Oc- 

 cipital furrow broadly rounded and rather shallow in the mid- 

 dle, becoming deeply impressed back of the posterior glabellar 

 lobes. Occipital segment without median tubercle or spine, 

 the posterior margin nearly parallel with the occipital furrow, 

 including a pair of small rather ill-defined occipital lobes lying 

 behind the posterior glabellar lobes. Fixed cheeks in front of 

 the eye-lobes divided into two, regions by the ocular ridges 

 which are prominent and describe a backward curve from 

 opposite the antero-lateral angles of the median glabellar lobe 

 to the eyes ; the inner region of the fixed cheek is narrowly sub- 

 crescentic in outline, lying opposite the lateral glabellar lobes, 

 and rather strongly convex; the outer region is strongly de- 

 pressed, extending in a nearly horizontal direction, sub-triangu- 

 lar in outline, becoming narrow posteriorly and also towards 

 the median point of the anterior cephalic margin, being widest 

 opposite the anterior lateral angles of the -cranidium. Eye- 

 lobes small, not well preserved. The posterior portion of the 

 fixed cheeks are produced laterally in elongate, slender points. 



