FOSSILS OF THE LOWER SILURIAN. 89 
PCECILOPODA. 
Genus DICELLOCEPHALUS Owen. 
Dicellocephalus finalis, n. sp. 
Plate xii, figs. 12, 12a, b. 
Form of glabella and fixed cheeks united, very irregular; front broad, 
rapidly contracting before and expanding at the eyelobes to contract again 
back of them. Glabella of about, the same width at the base and in front, 
expanding, on the posterior half, to the border of the palpebral lobes; gen- 
eral surface quite convex on the anterior half and moderately so farther 
back, marked by three pairs of glabellar furrows; the anterior pair slightly 
impressed and short, situated opposite the anterior end of the eyelobes; 
the median pair more strongly impressed and directed obliquely inward 
about one-fourth the distance across from side to side; directly back of this 
pair the margin curves outward around a curved expansion of the glabella, 
and within this the posterior pair of furrows are impressed, similar to the 
median pair, but not reaching the outer margin; this gives the posterior 
portion of the glabella a very peculiar aspect, unknown in any other species 
of the genus; occipital ring broad and flattened; occipital furrow narrow 
and well impressed; dorsal furrow distinct, but very shallow; fixed cheeks 
hardly more than a line, except where they join the broad frontal limb; 
palpebral lobes long and narrow; postero-lateral limbs narrow and extended 
laterally; frontal limb of moderate length, gently concave, and bordered 
by a strong rounded margin, the anterior edge of which is broadly rounded 
up to a very obtuse angle at the center. 
Thorax known only by fragments of the segments associated with the 
head parts. These show the median lobe to have been moderately convex 
and the lateral lobes less so; the pleure are straight or slightly curved two- 
thirds the way out, and then curved backward on the free end; pleural groove 
strongly marked. 
The associated pygidium is moderately convex, with a conical axial lobe 
crossed by three annulations, besides the long terminal one; lateral lobes 
