THE NATURAL HISTORY SURVEY. 25! 



Acidaspis vanhornei, n. sp., pi. xxin, figs. 3-4. 



Description. Cephalon, exclusive of the genal and median 

 spines, sub-quadrangular in outline, the breadth nearly twice 

 the length, the surface finely granular throughout. Glabella 

 sub-cordate in outline, depressed-convex, a little wider than 

 long, its greatest width at the middle of the posterior lateral 

 lobes, the. lateral lobes but little depressed below the median 

 lobe. Median lobe elongate sub-ovate in outline, narrowly 

 rounded in front, truncate behind, its greatest width about 

 one-half its length, its anterior lateral expansions scarcely 

 separated from the lateral lobes and coalescing with the ocular 

 ridges. Anterior lateral lobes minute, scarcely separated from 

 the anterior lateral expansions of the median lobe; the second 

 lateral lobes much larger, their axes directed obliquely outward 

 and forward; posterior lateral lobes about three times as large 

 as the second pair, sub-ovate in outline, their longer axes nearly 

 parallel with the median line of the cephalon; all the lobes 

 coalescing with the median lobe internally. Anterior pair of 

 lateral glabellar furrows scarcely distinguishable, second pair 

 deeply impressed, slightly curved and directed obliquely for- 

 ward and outward, extending to the dorsal furrow; third pair 

 less strongly impressed than the second, the innermost strongly 

 impressed portion directed nearly straight towards the front, 

 the outer portion bent obliquely outward. Dorsal furrows de- 

 scribing a gentle curve, strongest at their junction with the 

 occipital furrow, becoming faint anteriorly and scarcely recog- 

 nizable in front of the second pair of glabellar furrows. Occipital 

 furrow rather shallow back of the median glabellar lobe, be- 

 coming much more deeply impressed back of the lateral lobes. 

 Occipital segment sublunate in outline, broadest in the middle, 

 its lateral extremities becoming mere points just outside the 

 posterior ends of the dorsal furrows, it bears a single, long, 

 slender, median spine, which is directed backward with a slightly 

 convex curve. Cheeks sub-rhomboidal in outline, moderately 

 convex, their, postero-lateral angles extended into slender, 

 divergent, slightly curved genal spines, facial sutures not dis- 

 tinguishable. Eyes small, situated nearer the inner and pos- 

 terior margins than the lateral and anterior, connected ante- 

 riorly by narrow but well-defined ocular ridges with the an- 

 terior lateral expansions of the median glabellar lobe; the inner 

 area between the ocular ridge and the dorsal furrow is nar- 

 row, acutely pointed in front and strongly convex longitudin- 



