DESCRIPTION OF GENERA AND SPECIES. 179 
Genus PTYCHASPIS Hall. 
Ptychaspis HALL, 1863, 16th Annual Report New York State Mus. Nat. Hist., p. 170. 
Ptychaspis acamus Walcott. 
Plate 16, Figures 18, 18a. 
Ptychaspis acamus Wacortr, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 69. (Species described as 
below.) 
This species is represented by specimens of the glabella and fragments of the 
fixed cheeks. The glabella is moderately convex at the back and strongly convex 
on the frontal lobe; it is divided by a strong, backward-arching furrow, which sepa- 
rates the posterior portion as a transverse lobe, and the anterior as a large lobe 
about as long as broad; the latter is marked by two narrow, short, slightly impressed 
furrows on the sides of the lobe; occipital furrow strongly rounded, deep, and arching 
forward at the center; occipital ring about the middle of the posterior lobe of the 
glabella nearly flat, and with a small, sharp node at the center near the back margin; 
frontal rim a rounded, narrow border in front of the deep, narrow dorsal furrow; 
dorsal furrow narrow and deep opposite the palpebral lobe. 
Fixed cheeks rise rapidly from the dorsal furrow; they are narrow and convex; 
palpebral lobes unknown; the anterior lobe of the glabella slightly overhangs the 
dorsal furrow, which is deep and rounded. 
Surface marked with low, large pustules and very faint puncte. 
The type specimen of the cephalon in the collection has a length of 11 mm., 
with a width of 6 mm. 
This species is characterized by the form of the large frontal lobe, the strong 
transverse furrows, and narrow posterior lobe of the glabella, and its peculiar surface. 
The typical specimens of this species were referred in the original description to 
the Middle Cambrian, Ch’ang-hia formation. Further study and comparison with 
material from the upper part of the Upper Cambrian, Ch’au-mi-tién formation, 
lead me to think that it is highly probable that the specimens labeled as from the 
Ch’ang-hia formation were collected from the higher horizon of the Ch’au-mi-tién, 
and accidentally placed with material from the Ch’ang-hia. This is rendered 
more probable, as the two lots of specimens were collected at and near Ch’au-mi-tién. 
The specimens from the upper part of the Ch’au-mi-tién formation appear to be 
identical with the type, and from a lithologically similar limestone. In view of 
this, and the fact that the genus Ptychaspis is unknown from the Ch’ang-hia forma- 
tion, I have changed the reference to the Upper Cambrian, Ch’au-mi-tién formation. 
Formation and Locality—Upper Cambrian: (C45) Limestone about 4o feet 
(12 m.) below the top of the Ch’au-mi-tién limestone [Blackwelder, 19074, p. 36 
(part of third list of fossils)], at Ch’au-mi-tién, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Ptychaspis baubo (Walcott). 
Plate 17, Figures 2, 2a. 
Dikelocephalus (?) baubo WaLcorr, 1905, Proc. U.S. Nat. Mus., vol. xx1x, p.91. (Species described 
essentially as below.) 
The description of Ptychaspis brizo applies to this form, with the exception that 
P. baubo has a more rounded front to the glabella, and its frontal rim and border 
vary somewhat inform. In P. baubo the palpebral lobe is preserved, and shows it 
to have been relatively small and short, and marked just within the rim by a rather 
deep furrow. A cephalon of P. baubo 16 mm. in length has a glabella 12 mm. in 
length, frontal rim and limb, 2 mm., and occipital furrow and ring, 2 mm. in length; 
the glabella has a width of 9 mm. opposite the palpebral lobe. 
