120 RESEARCH IN CHINA. 



margin; frontal limb broad, concave, and rising with a gentle curvature from the 

 front of the glabella to the margin of the thickened frontal rim. 



Free cheek roughly subtriangular ; it is divided into an interior convex body, 

 which rises from the furrow at its base to the small eye-lobe at its center ; the border 

 of the cheek is crossed obliquely by a sharp ridge that extends from its inner, anterior 

 side backward to its outer side, where it forms the outer edge of a sharp spine ; 

 the border extends backward, but not so as to form the genal angle of the cheek; 

 a strong, sharp spine originates a little in advance of the facial suture and extends 

 obliquely backward. 



The type pygidium of this species was described as follows: 



Pygidium semicircular in outline, moderately convex, and with a spinose 

 margin; axis moderately convex, conical, with a broadly rounded posterior end; it 

 is divided by three clearly marked, transverse rounded furrows into a strong ante- 

 rior ring, next to the thorax, two moderately convex rings, and a long terminal 

 portion, which has a slight fourth depression, indicating a fourth ring; the posterior 

 portion of the axis slopes rather rapidly down to the margin; owing to an abrasion, 

 the presence or absence of additional rings or nodes usually present at the end of 

 the axis can not be determined. Dorsal furrow rounded and shallow. 



Pleural lobes flat for a short distance from the axis, and then curve gently 

 downward to the border; they are marked by a deep anterior furrow within the 

 narrow, anterior, elevated margin, and three furrows that terminate at the margin; 

 the furrows outline three rather broad, slightly convex segments and a posterior 

 area opposite the postero-lateral angle of the axis. The border is practically a 

 continuation of the slope of the segments and furrows of the pleural lobe ; it is marked 

 opposite the segments by five short, backward-pointing, flat, broad spines, and 

 diagonally opposite the lateral angle of the axis by two long, strong, backward- 

 extending spines; in addition, there are two short spines with broad bases back 

 of the axis between the two long spines. [Walcott, 19056, p. 27.] 



In a collection from another locality specimens of the pygidium show consider- 

 able variation. On the larger specimens the axis is divided by four well-defined, 

 strong transverse furrows and a fifth furrow is indicated by a shallow depression 

 across the terminal section ; the furrows divide the axis into five segments or rings, 

 and the subtriangular terminal portion that slopes rapidly from its center to the 

 thickened border; lateral lobes broad, convex, and marked by a narrow, anterior, 

 elevated segment, which joins the thorax, and three strong, narrow, elevated ridges, 

 and a small node indicating a fourth ridge; the ridges are separated by broad, strong 

 furrows that are continuations of the furrows crossing the axis ; the thickened border 

 is separated from the body of the pygidium by a shallow groove. 



Surface of the crust of the cephalon, free cheeks, pygidium, and associated 

 fragments of the segments of the thorax, minutely punctate. 



The largest cephalon in the collection has a length of 20 mm., with the same 

 width at the palpebral lobes; the largest pygidium has a width of 35 mm. and a 

 length of 1 8 mm., exclusive of the spines. 



This species was founded on a pygidium from the Ku-shan shale zone in Shan- 

 tung. A year later the same specific form of pygidium was observed in a new lot 

 of material from the Ku-shan shale horizon of Shan-si. With the Shan-si specimens 

 numerous cephala and free cheeks occur that are considered to belong to this species, 

 as there are no other forms occurring in the same rock to which the pygidia could 

 be referred. 



The cephalon of this species differs from that of Blacku'elderia siiioisis [plate 

 9, figs. 5, sa-b] in having a longer frontal limb, narrower fixed cheeks, and smoother 



