DESCRIPTION OF GENERA AND SPECIES. 181 
Ptychaspis brizo (Walcott). 
Plate 17, Figures 3-5. 
Dikelocephalus (?) brizo WaLcort, 1905, Proc. U.S. Nat. Mus., vol. xxx, p.92. (Species described as 
below.) 
This species is represented by the anterior portions of a large, moderately 
convex cephalon, exclusive of the free cheeks. The glabella is subquadrilateral, 
with the sides slightly incurved and the front nearly transverse; it is marked by a 
strong pair of posterior furrows that penetrate obliquely backward nearly to the 
median line; a second pair incline slightly backward and penetrate to about one- 
third the distance across; a third pair, narrow and very slightly impressed, extend 
in at right angles to the sides a little less than one-third the distance; occipital 
furrow well defined, with a slight, elongate, pit-like depression at the antero-lateral 
angles of the glabella. 
Fixed cheeks very narrow, not much more than a ridge opposite the palpebral 
lobes; palpebral lobes unknown; palpebral ridge rounded, and dividing the fixed 
cheek into the flat posterior portion and the rather rapidly sloping frontal portion 
that passes down into the concave frontal limb; frontal limb short, concave, and 
bordered by a rounded, thick frontal rim. 
Surface marked by numerous, more or less irregularly placed, strong pustules, 
except in the dorsal furrow and the concave frontal limb. 
The fragmentary specimens representing this species indicate a length for the 
glabella of 22 mm., with a width in front of 14 mm.; the concave frontal limb has a 
length of 2.5 mm., and the thickened rounded rim has a length of about 1.5 mm. 
The fixed cheek at the palpebral lobe has a width of 2 mm. 
The form of the glabella, frontal rim, and narrow fixed cheeks suggests Dikelo- 
cephalus, but the strongly pustulose surface is not characteristic of the typical forms 
of that genus. 
Formation and Locality—Upper Cambrian: (C38) Crystalline limestone near 
the base of the Ch’au-mi-tién limestone [Blackwelder, 19074, p. 36 (part of first list 
of fossils)], at Ch’au-mi-tién, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Ptychaspis cacus Walcott. 
Plate 17, Figures 10, 11. 
Ptychaspis cacus WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxrx, p.69. (Described as a new species 
essentially as below.) 
General form of cephalon, exclusive of the free cheeks, subrhomboidal, rounded 
in front, strongly convex. Glabella moderately convex over the posterior portion, 
strongly convex at the frontal lobe; the posterior portion is divided into two lobes, 
of about equal width, by the broad, rounded, transverse posterior furrow and a 
narrow, slightly impressed anterior furrow, both of which arch slightly backward 
toward the center; the frontal lobe is about as long as the two posterior lobes and 
arches with uniform curve over to the dorsal furrow; it is convex but not globose; 
it is marked about midway on each side by a short, very slightly impressed, narrow 
furrow, which penetrates it at right angles to the dorsal furrow; occipital furrow 
broad, strong, and arching slightly forward at the center; occipital ring about as 
wide as the posterior lobe of the glabella, moderately convex, and arching slightly 
forward near the center; dorsal furrow strongly defined at the sides and somewhat 
less so in front of the glabella; a shallow pit occurs opposite the antero-lateral angle 
of the glabella. 
