224 



Sculpture. 



Compared 

 with other 

 species. 



There is a narrow, sharp genal spine, of unknown length, projecting back- 

 ward from the outer angle of the cheek. 



The thorax has narrow rings with narrow pleurae, having sharp back- 

 ward-curved points. The thoracic rings have triangular lobes at the 

 outer ends and a median tubercle, like the occipital ring. The pleurae 

 have a sharp, oblique furrow, extending to the geniculation. 



A hypostome supposed to belong to this species has a large, oval anterior 

 lobe, narrower behind ; an upturned margin borders it at the sides, but 

 at the back is broken away. 



The pygidium has two well marked rings to the rachis, each sur- 

 mounted by a tubercle, and a posterior lobe which is obscurely divided 

 into two somites. The side lobes have two faintly marked ribs with 

 diagonal grooves, and the borders of the side lobes are flattened. A 

 small backward, outward projecting spine is placed at the anterior corner, 

 on each side. 



Sculpture. The area in front of the glabella is ornamented with 

 forking and anastomosing raised lines, radiating toward the anterior 

 margin. The glabella appears smooth, but under a strong lens is seen to 

 be minutely punctate, or even obscurely reticulate with raised lines. The 

 movable cheek, like the area in front of the glabella, is ornamented with 

 distinct raised lines, giving a reticulate surface : toward the marginal 

 fold these lines are forked and directed outwards. 



The reticulation of raised lines is more distinct on the interior than on 

 the exterior surface of the test. A similar but faint reticulation is visible 

 on the front half of the fixed cheek. The surface of the glabella, seeming 

 smooth to the naked eye, when viewed with a lens appears to the faintly 

 marked with scattered pits or depressions. The front and lateral marginal 

 fold of the head-shield, when viewed with a strong lens, is seen to be 

 minutely stria te lengthwise of the fold. 



Size. The head-shield figured is not the full size of this species, for 

 some pleurse sho -v that it grows to a size one-quarter longer. 



Horizon and locality. In limestone of Band C. 3b at Escasonie shore, 

 East bay. N.S. 



This species is closely allied to P. acanthura, Ang.,* from which it 

 differs in the following respects : The area in front of the glabella is 

 wider and more strongly arched, and the fixed cheek is more pointed at 

 the posterior outer angle. In the free cheek the rim is more strongly 

 arched in front, and has less width behind. The joints of the thorax 



*Palseontol. Scand., p. 49, pi. xxvi, fig. 9. Also Om Acerocare, Moberg & Moller, 

 Stockholm. 1898, p. 239' tafl. 12, figs. In and 4a. 



