498 
SILURIAN TRILOBITES, 
Sp. Char. — Body —Oblong oval. Head-shield or cephalon. — 
Subsemicircular, width rather greater than twice its length. 
Glabella, including the neck ring, about five-sixths of the greatest 
width, very slightly convex above, slightly subpentagonal, over- 
hanging very little in front, sides straight and steep, limb very 
rudimentary, and the furrow between it and the glabella faint ; 
three pairs of lateral grooves present, frontal pair passing out 
at the front angles and running obliquely across the glabella, 
terminating subfalcately ; second pair opposite posterior horns 
of eyes, both of these pairs are linear; intercalary groove 
moderately distinct, wide and shallow ; intercalary ring with 
well-marked nodules at each end; the whole glabella surface 
ornamented with various-sized granules, and wrinkled in front 
subvertically; neck furrow shallow, moderately distinct, and con- 
tinued across and round the side lobes, becoming very shallow as 
it reaches the borders, and continuing so in its frontal extension; 
neck ring distinct, ends nodular; axial furrows distinct and 
wide and genal lobes sloping rather steeply into them; lateral lobes 
subtriangular (equilateral), borders thickened, ridges along posterior 
faces between the axial furrows and fulcra robust; imbricating 
facets large; genal lobes highly convex and granulated, separated 
from the palpebral lobes by a faint furrow* which passes pos- 
teriorly around and under the eye, giving relief to that organ, 
and joining the lateral prolongation of the neck furrow and 
enclosing between them a suboblong tumose area or extension of 
the genal lobe. Eyes very large, half as long as posterio-anterior 
length of head, anteriorly almost resting on the cheek borders, being 
separated from them by the fainter lateral furrows only; normal 
number of vertical rows of lenses twenty-two, closely packed, toler- 
ably convex, with twelve lenses in each of the central rows, the total 
number of lenses in each eye being about 220; in the cups the 
attachment processes visible under a lens; cornea seems to have 
been thin; lentiferous face curved from front to back lunately, 
* This may be termed the palpebral furrow, and should perhaps be con- 
sidered a generic character. 
