October, 1913. New Trilobites — Slocom 79 



is three-fourths of its greatest width, and it has tubercles at the juncture 

 of the occipital and dorsal furrows; in S. maquokctensis the glabella is 

 twice as wide anteriorly as posteriorly and the tubercles are wanting. 

 Localities and horizons. — Abundant in the top layers and some- 

 what less so in the middle layers of the Lower Maquoketa shales of 

 Clermont, Elgin, and Bloomfield, Iowa. 



Family PHACOPID^, Salter. 



Genus PTERYGOMETOPUS Schmidt 1881. 



Cephalon obtusely angular in front. Glabella enlarging anteriorly, 

 lateral furrows well defined. Eyes large, schizochroal. Posterior limb 

 of the facial suture cuts the margin well in front of the genal angles, 

 and the anterior limb crosses the lateral expansions of the frontal lobe 

 of the glabella. Pygidium rounded, margin entire, without caudal 

 spine. Range, Ordovician of Europe and North America. 



Pterygometopus fredricki sp. nov. Plate XVIII, Figs. 1-5. 



Type specimen No. P 17024 Field Museum. 



Test elongate-ovate in outline, trilobation distinct. Cephalon sublu- 

 nate in outline, convex, anterior border rather thick and rounded, 

 posterior margin concave, genal angles rounded. Glabella large, con- 

 vex, greatest elevation and greatest width near the anterior margin, 

 well defined by the dorsal furrows; anterior lobe large, transversely 

 elliptical, rising abruptly from the anterior border; it comprises more 

 than half of the glabella; anterior pair of lateral furrows originating at 

 the anterior angles of the eyes, passing obliquely backward but not 

 crossing the glabella; second pair of lateral furrows smaller than the 

 first and directed obliquely forward forming a pair of triangular lateral 

 lobes; the third pair of lateral furrows bifurcate, the anterior forks 

 extending forward parallel to the second lateral furrows defining the 

 quadrangular second lateral lobes, the posterior forks extending back- 

 ward until they join the occipital furrow isolating the small, posterior, 

 glabella lobes ; occipital segment elevated at its posterior margin sloping 

 to the occipital furrow; occipital furrow narrow, distinct. Dorsal fur- 

 rows narrow and deep, nearly parallel from the posterior margin of the 

 cephalon to the third, lateral glabella furrows, thence diverging to the 

 antero-lateral margins. Cheeks slope regularly to the lateral margins; 

 marginal borders wide at the genal angles narrowing in each direction, 

 marginal furrows shallow on the lateral margins, deeper on the posterior 

 margins; palpebral lobes large, prominent, but not equaling the glabella 



