LOWER HELDERBERG ROCKS. 
369 
joining the frontal border, and forming with it a continuation of a 
similar border; the pustules, as they recede from the centre in front, 
gradually become stronger and assume the form of short spines, which, 
to the number of ten to fourteen, ornament the cheek border. The 
posterior angle is produced in the form of a long curving spine, on the 
inner margin of which, beyond the limits of the head proper, are one, 
two, or three short spines. 
Eyes nearly in a line with, or a little in advance of, the occipital furrow, 
subcylindrically ovoid; showing, under a lens, the minute facets upon 
the surface. 
The thorax (imperfect) has apparently nine segments : the axis is very 
prominent, and nearly one-third narrower than the lateral lobe ; the 
articulations marked by a node at each extremity, and one in the 
centre : lateral lobes of the axis having the articulations produced into 
a long rounded spine, which is bent abruptly backwards, and finally 
assumes a direction nearly parallel to the axis; each of the articula¬ 
tions marked by two strong nodes, one of which is at the point of 
retrorse bending of the rib, and the other nearer to the axis. The 
prolongation of the spine is two and a half to three times as great as 
the width of the lateral lobe. 
Pygidium, excluding the spines, somewhat semicircular, preserving three 
annulations in the axis, and marked posteriorly by a strong elevated 
rim. From the middle segment are produced two long spines at right 
angles to its direction, or parallel to the axis, and, between these, 
two shorter intermediate spines; while on each side, exteriorly to the 
long spines, are three others : the inner one is essentially parallel to 
the long spines, while the outer ones are divergent, and originate in a 
bifurcation of the rib. The middle annulation is marked by three nodes 
in its central portion; while the long spines each have two strong 
nodes near their origin, and similar smaller nodes mark the origin of the 
outer spines. The posterior segment has two small nodes on each side, 
with the centre plain. 
[ Paleontology III.] 47 
