DESCRIPTION OF GENERA AND SPECIES. 223 
This species appears to be most nearly related to [llenurus eurekensis Walcott 
[1884b, p. 97, plate 12, figs. 4, 4a], which occurs at the base of the Ordovician in the 
Iyureka district of Nevada, but it differs in the smaller palpebral lobes, which are 
situated farther back on the cephalon; and it differs from I. ceres [plate 23, fig, 4| 
in its proportionately longer cephalon. 
The species is widely distributed in the Upper Cambrian limestone. 
Formation and Locality —Upper Cambrian: (C38) Crystalline limestone near the 
base of the Ch’au-mi-tién limestone [Blackwelder, 1907a, p. 36 (part of the first list 
of fossils)], at Ch’au-mi-tién; (C34) purplish-gray limestone about 100 feet (30 m.) 
above the base of the Ch’au-mi-tién formation [idem], in road at northeastern corner 
of small village near Ch’au-mi-tién; (C42) in the central part of the Ch’au-mi-tién 
limestone [idem (second list of fossils)], 1.8 miles (2.9 km.) west-southwest from the 
temple on Tsing-lung-shan, 7.5 miles (12 km.) east of Ch’au-mi-tién, and (C41) 
lower part of the Ch’au-mi-tién limestone [idem (part of the first list of fossils)], 2.7 
miles (4.3 km.) southwest of Ch’au-mi-tién, Shan-tung; also (C54), lower part of 
Ch’au-mi-tién limestone [idem, p. 42 (part of last list of fossils)], near top of lime- 
stone knoll two-thirds of a mile (1.1 km.) west of Tsi-nan, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Illanurus ceres Walcott. 
Plate 23, Figures 4, 4a. 
Illenurus ceres WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. Xxrx, p. 97. (Described as a new species 
essentially as below.) 
Cephalon, exclusive of the free cheeks, rounded subquadrate, moderately con- 
vex; the posterior margin of the cephalon curves slightly upward opposite the 
glabella, where there is a slight thickening which gives the appearance of a narrow 
occipital ring; the front margin of the cephalon is broadly curved. Glabella very 
faintly outlined on the interior of the cast; as thus shown it has a width at the 
base of 6 mm. and at the front of 4.5 mm. on a cephalon 11 mm. in length; its 
somewhat rounded front is about 1 mm. from the frontal rim of the cephalon; no 
traces of glabellar furrows have been observed, and in only one specimen can the 
very faint dorsal furrow that outlines the glabella be seen. 
Fixed cheeks of the same specimen 3 mm. in width at the palpebral lobes, from 
which they extend with almost uniform width to the front, and broaden slightly back- 
ward before merging into the short, triangular postero-lateral limbs; palpebral lobes 
small and situated back of a line passing through longitudinal center of cephalon. 
The associated pygidium in the same fragment of rock is rounded subtriangular 
in outline, moderately convex, and without any indication of an axis except a very 
narrow, slightly marked median ridge on the cast of the interior. A specimen 11 mm. 
in length has a width of 16 mm. at the front margin; a very slight elevation of the 
front margin near the center indicates that the axial lobe of this specimen had a 
width of about 6 mm. 
Surface minutely but not closely punctate under a strong lens. 
This species differs from J. canens by the greater width of the cephalon at the 
palpebral lobes and less convexity; the associated pygidium is less convex, more 
subtriangular in outline, and without the indication of a central axis. 
The associated species on the same hand specimen are Ptychaspis ceto and 
Coosia carme. 
Formation and Locality—Upper Cambrian: (C38) Crystalline limestone near 
the base of the Ch’au-mi-tién limestone [Blackwelder, 1907a, p. 36 (part of first 
list of fossils)], at Ch’au-mi-tién, Shan-tung, China. 
Collected by Eliot Blackwelder, 

