730 THE PALEONTOLOGY OF MINNESOTA. 



I PtorygometopvB schmnlii. 



The cephalon is short, but pointed at the anterior extremity and bears a 

 depression at the meeting of the facial sutures, as in P. intermcdius. Cheeks quite 

 narrow and the angles produced into very short, round spinules. Glabella likewise 



Fig. 50. Cephalon of Pteryyometopus 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. intermedium 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. Eyes 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 Pkacops. 



The pygidia associated with these heads are similar to that of P. callicephalua of 

 the Trenton limestone of New York, having a rounded subtriangular outline, narrow, 

 very gradually tapering axis and broad, evenly convex pleura-. 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 



