CAMBRIAN" TRILOBITES WALCOTT 3 1 



about one-fourth the width of the glabella, gently convex and merg- 

 ing into the anterior and posterior limbs; the posterior limb is 

 about twice as long as deep below the eye lobe and marked by a 

 strong furrow within the broad, slightly convex posterior border ; 

 palpebral lobe small, 7 mm. long in a cephalon having a length of 

 35 mm. at the eye lobes ; it is bordered by a rounded rim that con- 

 tinues obliquely forward across the fixed cheek and merges into the 

 side of the glabella. Free cheeks large, gently convex ; bordered by 

 a rounded rim that is continued posteriorly into a spine ; posterior 

 margin rather broad and about one-third the length of the margin 

 between the genal angles and the occipital ring; eye lobe small and 

 not high. The genal spine is situated some distance out from the 

 central axis, so that it clears the terminal spines of the thoracic 

 pleurse. 



Thorax with seven nearly transverse segments ; axial lobe con- 

 vex, with the segments slightly rounded and a small node at the 

 center of each ; a low, narrow, transverse ridge occurs on each side 

 near the union of the axial and pleural lobes ; pleural lobes a little 

 wider than the axial lobe and slightly convex ; the pleura is straight, 

 out to the backward curving, terminal spine; the narrow pleural 

 furrow originates at the inner end next to the axis and passes 

 obliquely outward, terminating just back of the center of the pleura 

 at the base of the terminal spine; the latter has a strong base and 

 narrows rapidly to a sharp point as it extends outward and back- 

 ward a short distance. 



Pygidium large, moderately convex ; anterior margin nearly trans- 

 verse, posterior outline broadly semi-elliptical ; axial lobe convex 

 and narrowing gradually from the anterior margin to the terminal 

 ring at the narrow posterior border; it is divided into ten strong, 

 rounded, transverse rings and a terminal section by ten narrow 

 furrows ; the terminal section in large specimens has a transverse 

 pit on each side of its center that indicates an eleventh ring; a low 

 node is indicated at the center of each ring, and a low. narrow, trans- 

 verse swelling occurs near the dorsal furrow on each side; in a 

 pygidium 8 mm. in length there are nine clearly defined, axial rings, 

 a faint, tenth ring, and an elongate, rounded, terminal section ; pleural 

 lobes slightly convex out to the spinose border, which is flattened 

 between the termination of the pleural grooves and its outer edge; 

 the eight marginal spines on each side are similar to those of the 

 pleural lobes of the thorax with the exception of the posterior ones, 

 which extend directly backward; the space between the axial lobe 

 and the margin is marked by the pleural furrows and the narrow 



