FOSSILS OF THE LOWER SILURIAN. 



PCECILOPODA. 

 Genus DICELLOOEPHALUS Owen. 



Dicellocephalus finalis, n. sp. 

 Plate xii, figs. 12, 12 a, &. 



Form of glabella and fixed cheeks united, very irregular; front broad r 

 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 pleurae 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 



