TRENTON LIMESTONE. 247 
304, 1. PHACOPS CALLICEPHALUS. 
Pu, LXV. Figs. 3 a7. 
Compare Phacops Dalmanii, PortiocKk, Geol. Rep. Londonderry, pag. 282, pl. 2, fig. 7 a, b,c; and pl. 3, fig. 7 d. 
Also Phacops Murchisonii, pl. 2, fig. 9 a,b; and pl. 3, fig. 9 ¢, d. 
Buckler somewhat semicircular or sublunate, convex, produced at the posterior angles 
into a broad rounded wing-like expansion ; glabella broad and rounded in front, narrowing 
posteriorly, and three-lobed upon each side, the lower lobe short, with a tubercle at the 
base, or between it and the posterior angle of the eye; anterior angle of the eye reaching 
to the groove between the frontal and second lobe of the glabella ; eyes lunate, reticulated, 
elevated to the same line as the most prominent part of the glabella; thorax with eleven 
articulations, the lateral ones grooved; caudal shield rapidly tapering, with fourteen or 
fifteen articulations in the axial lobe, and nine in each lateral lobe ; the latter are distinctly 
grooved, and all terminate in a smooth border. Surface of the buckler pustulose-punctate ; 
of the articulations, less distinctly marked. 
This is a beautiful little species, bearing a very close resemblance to the Phacops dalmanit 
cited above; the only essential difference being in the small tubercles between the last 
lobe of the glabella and the posterior angle of the eye, which are not mentioned in that 
one, and the number of articulations in the caudal shield, which are, in Portiock’s species, 
nine in the central, and six in the lateral lobes. 
The surface of the buckler is very beautifully marked with small rounded pustules, the 
surface of which, and the spaces between, are finely punctulate ; differing in this respect 
from any other species. The axial lobe of the thorax has the surface marked with elongated 
or irregular pustules, with fine puncte ; while the lateral lobes are more finely papillose 
or granulate, and the same characters are more or less distinct in the caudal shield. It is 
the only species of the genus known to me in our lower strata, and differs from Puacops, as 
restricted by Emmricu, in having more than eleven articulations in the caudal shield. It 
must be regarded, however, as one of the earliest representatives of that type, which 
afterwards became more numerous, and varied in form, in the higher paleozoic strata. In 
this species the thorax and caudal shield have the characters of CaLyMENE, and it would be 
difficult to determine from these alone the true nature of the fossil. The eyes are as distinctly 
marked as in any of the subsequent species, and the direction of the facial suture is the same. 
Fig. 3 a. Cephalic shield of this species. The specimen is well preserved, and shows the extension of 
the posterior angles in a very perfect manner. 
Fig. 3 5. A small entire specimen of the same species. 
Fig. 3 c. The caudal shield, showing the number of articulations, etc. 
Fig. 3 d. A magnified portion of the surface of the buckler, showing the pustulose-punctate character 
of the surface. 
Fig. 3 e. A magnified portion of the articulations of the thorax, showing the irregular pustulose surface. 
Fig. 3 f Lateral view of the eye of this species. 3 g. Magnified view of the eye. 
Fig. 34, A contracted specimen. The lobes of the glabella are obliterated, and the surface of the eye 
