248 PALEOZOIC PALEONTOLOGY. a 
ARTHROPODA. 
TRILOBITA. 
PROETUS PACHYDERMATUS Barrett. 
Plate XXII., Figs. 16-21. 
1878. Proetus pachydermatus Barrett, Am. Jour. Sci., 3d ser, vol. 
KV. p87. 
Description.—Head semi-circular in outline, with a broad, flattened 
marginal border, the genal angles produced into sharp spines. Gla- 
bella subtriangular, with a pair of small, disconnected, ovoid basal lobes ; 
obtusely pointed in front, bordered by a sharply-defined dorsal furrow ; 
the first and second pairs of lateral furrows are rather faint, slightly 
curved and directed obliquely backward from the margin of the gla- 
bella; the third pair more prominent, curved, directed backward and 
connecting with the occipital furrow by a less sharply-defined depres- 
sion. Cheeks convex to the marginal border, the eyes opposite the third 
pair of lateral glabellar furrows. Facial sutures making a sigmoidal 
curve from the anterior margin of the head to the front of the eye-lobe, 
and after passing around the eye, bending outward and cutting the 
posterior margin near the base of the genal spines. Occipital segment 
broadened in the middle with a small median tubercle. Thorax un- 
known. Pygidium semi-elliptical in outline, broader than long, with 
a broad, flattened marginal border; the axis much elevated, occupying 
about one-third the entire width in front, tapering gradually to the 
obtusely-rounded extremity which hes just within the flattened border, 
divided into thirteen or fourteen segments; the plure strongly convex 
to the flattened border, divided into eight or nine sharply-grooved 
segments, which become obsolete at the marginal border. 
The entire surface of the glabella, except the lateral furrows, also 
the axial portion of the occipital segment, covered with fine, irregular 
papille; the anterior portion of the cheeks is covered with elongate, 
raised, vermiform markings, which become shorter and papillose pos- 
teriorly. The marginal border and genal spines are smooth, except 
on the edge, where they are covered with fine, elongate, raised lines. 
The axial and pleural segments of the pygidium are papillose, the 
