80 Field Museum of Natural History — Geology, Vol. IV. 



in height; marked by a distinct furrow just within and parallel to the 

 borders of the eyes; eyes large, lunate, extending from the posterior 

 cheek furrows to the anterior glabella furrows, eye facets arranged -in 

 vertical rows of five facets each; the facial sutures originate on the 

 lateral margins in front of the genal .angles,, curve inward with a sigmoid 

 curve to the posterior angles of the eyes, follow the inner margin of the 

 eyes to their anterior angles and thence pass forward to the anterior 

 margin of the cephalon. 



Thorax distinctly trilobed, composed of eleven segments. Axis 

 convex, occupying somewhat more than one-third the width of the 

 thorax; the pleural segments extend outward from the dorsal furrows 

 for a little more than one-third their length, from which point they bend 

 backward and abruptly downward to the lateral margins; extremities 

 rounded; a straight groove originates near the anterior edge of each of 

 the pleural segments at the dorsal furrows, extends slightly backward 

 and outward and becomes obsolete on. the flattened surface of each 

 segment. The dorsal furrows converge slightly to the ninth thoracic 

 segment, then more rapidly to the pygidium. 



Pygidium subsemicircular in outline, slightly produced posteriorly, 

 strongly trilobed. Axis narrow, convex, margins slightly incurved, 

 abruptly rounded posteriorly; there are ten sinuous annulations; dorsal 

 furrows narrow and deep, entirely surrounding the axis; the pleural 

 lobes, consisting of six to eight segments, each bearing a median groove, 

 curve slightly upward in their anterior portion, then downward to the 

 margins. The segments are defined by grooves which are distinct in 

 the anterior portion of the pygidium but gradually become obsolete 

 posteriorly. This feature is more noticeable in young specimens. Both 

 segmentation and median grooves become obsolete a short distance 

 from the margins, thus leaving a smooth, undefined, marginal border. 



The surface of the thorax and pygidium appears smooth to the eye, 

 but under a magnifier is finely punctate, without nodes or spines. The 

 surface of the cephalon is pustulose, the pustules on the glabella being 

 somewhat more prominent than on other parts. 



The dimensions of the type specimen (Mus. No. P 17024) are as 

 follows: Length, 24.2 mm.; width at genal angles 11.5 mm.; length of 

 cephalon on median line 6.7 mm. ; length including genal angles 7.4 mm. ; 

 length of thorax 11.5 mm.; length of pygidium 6 mm.; greatest width of 

 pygidium 8.7 mm. A detached pygidium (Mus. No. P 16923A) 

 measures, length 11.0 mm.; greatest width 14.6 mm.; it has ten annula- 

 tions in the axis and eight segments in each pleural lobe, the last two 

 being visible only with a magnifier. This is the largest pygidium 

 observed and appears to belong to an old individual. 



