TRILOBITES. 717 
Thaleops ovata.] 
General form ovoid, broadest anteriorly, attenuate and salient at the angles of 
the cephalon. Axial length and greatest width equal. Cephalon broadly semicir- 
cular on the anterior margin, slightly incurved or contracted laterally and again 
prominent at the genal angles which are narrow and produced beyond the general 
outline of the body into blunt, short spines. -Posterior margin gently convex on the 
cheeks and much more convex axially. Dorsal furrows clearly defined on the 
posterior half of the cephalon, disappearing at or in front of its summit. On internal 
casts these furrows are quite deep and though becoming faint anteriorly may some- 
times be traced nearly to the front margin of the shield. The glabella thus outlined 
is subquadrate, expanded anteriorly, its median width being about one-third the 
entire width of the cephalon. Where faintly delimited on its anterior portion its 
width is one-third greater than at its base. A single pair of very short lateral 
glabellar furrows makes a slight indentation on each margin, serving to divide 
the part into an anterior or frontal lobe and a single pair of lateral lobes. The 
_ occipital furrow and ring which are scarcely discernible on the outer surface are 
clearly distinguishable upon the cast. The anterior slope of the glabella is deep, 
nearly vertical for a short distance and convex above. The fixed cheeks are less 
convex than the glabella and along the dorsal furrows on the cast, bear an indenta- 
tion opposite and corresponding to the lateral lobes of the glabella. The general 
surface tapers to the narrow, subcylindrical palpebral lobes which are depressed 
below the rest of the surface and lie nearly in the plane of the thorax. The free 
cheeks are abruptly constricted beneath and in front of the eyes and take the form 
of divergent slightly recurved spines or horns. The facial sutures rise rapidly from 
the occipital margin to the summit of the eye-nodes, thence rounding gradually 
forward to the anterior margin which they intersect opposite the anterior extremities 
of the torsal furrows. 
Fig. 25.—Internal cast of Thaleops ovata Conrad. 
Thorax subquadrate, tapering; composed of ten segments. Surface strongly 
lobed. Axis convex, narrow. Pleurz geniculated at about one-third their length. 
Segments flat and, upon the axis, moderately broad, not furrowed on the pleure, 
recuryed toward their extremities. 
