730 THE PALEONTOLOGY OF MINNESOTA, 
[Pterygometopus schmidti. 
The cephalon is short, but pointed at the anterior extremity and bears a 
depression at the meeting of the facial sutures, as in P. intermedius. Cheeks quite 
narrow and the angles produced into very short, round spinules. Glabella likewise 
Fig. 50.—Cephalon of Pterygometopus schmidti. 
short, the frontal lobe covering more than one-half its length. It is, however, 
proportionally wide anteriorly, the dorsal furrows approaching rapidly so that the 
glabella at its base is but one-third its width in front of the eyes. The first lobes 
are narrow, transversely triangular, their general direction being obliquely forward 
toward their distal extremities. The second lobes are quite small, transverse and 
subrectangular, directed obliquely backward; the third lobes are two very obscure 
tubercles. The general surface of the glabella is regularly convex, there being no 
depressed area between the inner extremities of the first and second lobes. None 
of the lobes are confluent. The first glabellar furrows are transverse and concave 
anteriorly, while in P. intermedius they are convex. All these glabellar lobes are 
clearly defined and show no tendency to obsolescence. Occipital groove narrow, 
occipital ring also relatively narrow and not greatly elevated. Hyes proportionally 
very large, extending from the first glabellar furrows to the occipital ring. The size 
of these organs renders both the fixed and free cheeks remarkably small. Between 
the base of the eyes and the lateral margins is a broad, smooth, thickened but not 
elevated area. The entire surface of the glabella, the palpebral lobes and a small 
triangular area at the base of the eyes between the occipital ring and the border, is 
coarsely and abundantly tubercled. More scattered and finer tubercles are seen on 
the marginal border. 
The thoracic segments show no differentials of importance. ‘Their extremities 
are obtusely rounded as in Phacops. 
The pygidia associated with these heads are similar to that of P. callicephalus of 
the Trenton limestone of New York, having a rounded subtriangular outline, narrow, 
very gradually tapering axis and broad, evenly convex pleure. There is, however, 
a difference in the segmentation of the parts, the axis having 8—10 annulations 
which make a double sigmoid curve, and the pleura having 5—6 ribs, which are 
simple for about one-fourth of their length and then bifurcate. None of the ribs 
are continued to the margin which is broad and smooth. In sharp internal casts there 
are but four duplicate ribs, the posterior division of each disappearing toward the 
margin much sooner than the anterior. Behind these may be seen the trace of 
