ORDOVICIAN FAUNAS. 193 
tion nearly obsolete. Head subtriangular to semi-elliptical in outline, 
convex, slightly flattened in front; the anterior margin rather sharply 
rounded; facial sutures meeting at an angle, at or just behind the 
frontal margin, from this point they describe a broad, subarcuate 
curve, and, after passing around the eyes, they curve outward and 
then downward, intersecting the posterior margin at some distance 
outside of the eyes; glabella obscurely defined and more obscurely 
lobed; occipital furrow and segment obsolete; free cheeks marked 
by an intramarginal furrow, above which their general surface is 
elevated into a more or less conspicuous node, crowned by the eye. 
Thorax with a broad axial lobe, occupying more than one-third the 
width, consisting of eight segments. Pygidium subtriangular in out- 
line, of nearly the same size and shape as the head, its lobation very 
obscure, especially in the larger individuals, the dorsal furrows being 
hardly distinguishable; axis much narrower at its anterior extremity 
than the axis of the thorax, tapering rapidly to the obtusely rounded 
posterior extremity, which lies at about one-fourth the length of the 
pygidium from the posterior margin; plure convex, smooth in the 
larger individuals, but in younger ones marked by about ten obscure 
segments, which also continue across the axis; the entire margin of 
the pygidium, except where it joins the thorax, bordered by a rather 
broad, slightly depressed, marginal border; the anterior, lateral angles 
bent abruptly downward. 
Remarks.—No complete individuals have been observed, but frag- 
ments of heads, pygidia and thoracic segments of this species are not 
uncommon in the Trenton limestone of New Jersey, some of them indi- 
cating individuals which must have had a total length of over 150 mm. 
PTYCHOPYGE JERSEYENSIS Nn. sp. 
Plate XIV., Fig. 16. 
A single imperfect pygidium from Jacksonburg is apparently refer- 
able to this genus, and as it can. be referred to none of the described 
species, the above name is proposed for it. The general form of the 
pygidium is semi-elliptical. The plure are convex near the axis, 
becoming concave in the outer half; they are marked by four well- 
defined furrows, which extend almost to the margin. The segments 
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