360 SYSTEMATIC PALEONTOLOGY 



straight sides and a narrow margin in front; neck furrow extending 

 entirely across; three pairs of glabellar furrows directed slightly back- 

 ward, their inner extremities separated by about one-third the width of 

 the glabella. Fixed cheeks covered with small tubercles and separated 

 from the glabella by a deep groove on each side. 



Pygidium 6 mm. long and about the same at its greatest width ; front 

 margin rounded and the posterior somewhat straight. Axis conical and 

 strongly convex with five or six well-defined segments. Pleurae of the 

 pygidium five on each side and nearly parallel with the axis in their 

 posterior half, then curving inward to join the axial segments. 



Identified somewhat doubtfully in the Middle Beekmantown (Cera- 

 topea zone) in the Appalachian Valley of Maryland and southern Penn- 

 sylvania. Imperfect pygidia with the characteristic pleurae were observed 

 in exposures along the Cumberland Valle} r Kailroad northeast and south- 

 east of Halfway, Maryland. 



Occurrence. BEEKMANTOWN LIMESTONE (Ceratopea zone) . Halfway, 

 Maryland. 



Collection. IT. S. National Museum. 



Family PHACOPIDAE 



Genus PTERYGOMETOPUS Schmidt 



PTEKYGOMETOPUS CALLICEPHALUS (Hall) 



Plate XLIII, Figs. 18-21 



Phacops callicephalus Hall, 1847, Pal. New York, vol. i, p. 247, pi. Ixv, 



figs. 3a-l. 

 Pterygometopus callicephalus Clarke, 1894, Geol. Minnesota, vol. iii, pt. 2, 



p. 731, text figs. 51, 52; p. 732. 

 Pterygometopus callicephalus Weller, 1903, Geol. Surv. New Jersey, Pal., 



vol. iii, p. 206, pi. xv, figs. 29-32. 



Description. " Head sublimate in outline, obtusely subangular in 

 front, genal angles broad and rounded, with no indication of spinules. 

 Glabella large, depressed-convex, broad and rounded in front, becoming 

 much narrower behind; frontal lobe large, subelliptical in outline; 



