THE NATURAL HISTORY SURVEY. 271 



glabella. Eyes generally large, always with distinct facets, 

 schizochroal. Thorax of eleven segments, with grooved pleura. 

 Pygidium usually large and of many segments; limb ribbed; 

 margin entire or dentate." Beecher, Zittel-Eastman Text 

 Book of Paleontology, p. 636. 



Genus 20. PHACOPS Emmrich, 1839. 



Entire body sub-ovate or sub-elliptical in outline. Cephalon 

 sub-semicircular, the genal angles usually rounded; glabella 

 strongly convex, very broad and expanded in front, the two 

 anterior pairs of lateral furrows inconspicuous or obsolete; 

 free cheeks more or less completely anchylosed with the fixed 

 cheeks so that the facial sutures are frequently obscure; eyes 

 large and prominent, with distinct, large facets. Thorax t with 

 strong axial furrows, segments eleven or twelve in number. 

 Pygidium semi-circular with entire margin. 



Phacops handwerki, n. sp., pi. xxiv, figs. 6-7. 



Description. Entire body sub-elliptical in outline, tapering 

 posteriorly. Cephalon semi-circular with rounded genal angles; 

 glabella gently convex, sub-quadrangular, the anterior margin 

 arcuate, reaching to the anterior marginal border of the cephalon, 

 narrowest at its posterior extremity where it occupies about one- 

 third of the entire width of the cephalon ; lateral furrows of the 

 glabella obsolete except the posterior ones which are narrow 

 and deeply impressed and extend across the entire width of 

 the glabella; the posterior lobe of the glabella very narrow 

 with a small rounded node at each end, depressed between the 

 large frontal lobe and the occipital segment. Occipital furrow 

 narrow but rather deeply impressed. Occipital segment strongly 

 arched transversely, the surface sloping with a convex curve 

 into the occipital furrow. Cheeks sub-triangular, the facial 

 sutures indistinguishable, the palpebral lobes large, their outer 

 margins elevated to the height of the glabella; eyes very large, 

 their length equaling one-half the length of the cephalon, the 

 height of the faceted portion two-thirds their length; the outer 

 portion of the cheeks sloping away from the eyes rather abruptly 

 with a slightly convex curve. 



Thorax strongly trilobate with eleven grooved segments; 

 the axis arched transversely, occupying one-third the width of 

 the body, tapering slightly to the posterior extremity; the 

 inner half of the pleural lobes flattened with the surface nearly 

 horizontal, the outer portion bent abruptly^downward. 



