224 RESEARCH IN CHINA. 
Illenurus dictys Walcott. 
Plate 23, Figures 5, 5a. 
Illenurus dictys WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxx, p. 98. (Described as a new species 
essentially as below.) 
Cephalon, exclusive of the free cheeks, rounded, subquadrate, gently convex; 
the posterior margin of the cephalon curves slightly upward opposite the central 
portion, where there is a slight elevation which gives the appearance of a narrow 
occipital ring; the front margin of the cephalon is broadly rounded, with a very 
broad, obtuse angle at the center; the cast of the interior of the crust shows a very 
faint, low, longitudinal median ridge. The glabella is not defined from the fixed 
cheeks. ‘The palpebral lobes are small and situated nearly opposite the center of 
the cephalon; postero-lateral limbs small and short. 
Surface smooth under a strong lens. 
The associated pygidium is transverse, rounded, subtriangular; front broadly 
rounded; sides gently rounded, forming a rounded obtuse angle at the posterior 
margin; the cast of the interior of the crust shows a narrow, slightly defined axis, 
with eight or more very faint transverse furrows and rings. The pleural lobes are 
gently convex and without any trace of furrows. 
A cephalon of 6 mm. in length has an equal width at the palpebral lobes. A 
specimen of the associated pygidium 7 mm. in length has a width of 8 mm. at the 
frontal margin. 
This species differs from Illenurus ceres [p. 223] in the obtusely pointed frontal 
margin of the cephalon and its less convexity. From Jllenurus canens [p. 222] it 
differs in the direction of the facial sutures from the frontal margin back to the 
palpebral lobes; the sutures of Illenurus dictys extend slightly outward from the 
base of the palpebral lobe to the margin, while those of [/lenurus canens extend 
directly forward, making the central portion of the cephalon narrower at the frontal 
margin. 
Formation and Locality.—Upper Cambrian: (C56) Lower part of Ch’au-mi-tién 
limestone, 25 feet (7.5 m.) below the top of Pagoda Hill [Blackwelder, 1907a, p. 42 
(part of last list of fossils)], 1 mile (1.6 km.) west of Tsi-nan, Shan-tung, China. 
Collected by Eliot Blackwelder and Li San. 
SEPARATED PYGIDIA. 
There are several genera and a number of species represented in the collections 
by pygidia which can not readily be referred to any known cephala. It is thought 
best to indicate such by generic reference as far as possible, but not to give specific 
names, thus avoiding duplication where the cephala of the same species may have 
been described from other localities and by other authors. Where the separated 
pygidia are associated with cephala considered to belong to the same genus, they 
are placed next to the cephala on the plate, and notes made of their relations in the 
description of the plate. 
There are also a number of free cheeks which are not associated with the 
central portions of the cephalon of any species to which they can be assigned. A 
number of these have been generically identified, and will be referred to in the 
description of the plate upon which they are figured. 
