496 
SILURIAN TRILOBITES, 
and small; intercalary ring nodular; axial grooves deep and wide; 
neck furrow distinct, and continued across the lateral lobes very 
distinctly; neck ring robust and bearing centrally a spine of 
varying size, corresponding with the thoracic axial spines, bases 
nodular ; lateral lobes small, triangular, tumid, borders thickened, 
their measurement from genal angles to the front of the axial 
grooves equal to half the front width of the glabella; posterior 
facets strongly ridged; palpebral lobes conspicuous, highly arched, 
outwardly bounded by distinct narrow borders, granulate; palpe- 
bral grooves very distinct, deep at front and back and thus 
contracting the genal lobes, passing posteriorly round and under 
the eyes into the lateral extensions of the neck furrow, adding 
relief to that organ; genal lobes tumid and deltiform; genal angles 
rounded and faceted; when the thickened borders fall out deep 
grooves are left. Eyes equal to half the length of cheeks, seventeen 
rows of lenses, the maximum number in a row being five; cornea 
and walls of cups thick; lentiferous face, an term-posteriorly, has a 
semicardiod curve. 
Thorax — As wide as long, very gently contracting posteriorly, 
sides almost perpendicular, smooth; axis sharply ridged, rings 
nodular at bases and centrally bearing strong, short recurved 
spines; when decorticated it is semicylindrical, as wide as 
side lobes (not measuring the contour of lobes); axial furrows 
moderately distinct; side lobes horizontal between axial grooves 
and fulcra, pleurce slightly recurved, ends rounded in at the 
posterior angles; medial grooves distinct, reaching beyond the 
middle of the deflected ends in decorticated specimens, and 
triangular posterior ridges strong; little or no trace of granulation 
on any portion of the thorax. 
Pygidium. — About semicircular, highly inflated; axis very 
prominent anteriorly, and terminating indistinctly at the inner 
edge of the border at about half of its anterior width, slightly 
depressed between the side lobes, shows eight rings and a 
terminal piece; the first three rings bear nodules centrally corres- 
ponding to the spines of the thoracic axis and are arched forward; 
each succeeding one becomes less distinct until the last is very 
