I'OSSILS OF THE WAVEKLY C4ROUP. 263 



the glabella equal to one-half its width at the anterior end, and rounding 

 inward with a gentle curvature to the anterior side of the palpebral lobe, 

 the cheek being very narrow at this point, thence passing along the top 

 of the eye to the junction of the posterior lateral limb. Surface of the 

 glabella and cheeks smooth, except a few granules near the base of the 

 glabella. 



Movable cheeks of medium size in proportion to the glabella, flattened 

 convex from the base of the eye to the narrow, thickened, and chamfered 

 marginal rim; occipital furrow narrow, not strongly marked, and reaching 

 nearly to the depression within the marginal rim ; posterior angles of the 

 cheeks extending backward in the form of short angular spines. 



Thoracic segments unknown. 



Pygidium paraboloid in outline, highly convex, abruptly so at the 

 sides and posteriorly. Axial lobe forming a little less than one-third of the 

 entire width, and reaching nearly to the posterior margin, rounded and 

 strongly elevated throughout; gradually tapering posteriorly and narrowly 

 rounded at the extremity; marked by from fifteen to seventeen annulations 

 in different individuals exclusive of the anterior articulating ring. Lateral 

 lobes well marked, very convex, slightly flattened near the axis, but very 

 abrupt at the sides and behind ; marked by from fourteen to sixteen very 

 sharply elevated angular ribs, which occupy the entire border, extending 

 beyond the end of the axial lobe, and reaching almost to the margin, leaving 

 only a narrow plain' space at the edge. The surface of the annulations is 

 marked by a series of small nodes, or pustules, along their crests, arranged 

 in four longitudinal rows on the axial rings, and an indefinite number, 

 closely arranged, occur on those of the lateral lobes. 



The species in some of its features resembles P. macrocejjhalus Hall of 

 the shales of the Hamilton group of Kew York, especially in the markings of 

 the pygidium ; but it difi'ers in the more elongate form and number of ribs 

 of this part, while the glabella is proportionally narrower and the sides 

 more nearly parallel ; the fixed cheeks and anterior border are narrower, 

 and the movable cheeks terminate in spines, which is not the case with that 

 one. The surface of the glabella and head is also destitute of the strong 

 pustules which characterize that species. 



