VOL. XX. (3) THE SILURIAN ROCKS OF MAY HILL 
219 
Description of two Trilobites, by 
Dr. F. R. Cowper Reed, Sc.D., F.G.S. 
Lidias Maia, sp. nov. 
Description . — Pygidium transversely semi-elliptical ; margin 
regularly curved, entire, not interrupted by any projecting 
pleural points ; surface gently convex from side to side and 
more strongly so from back to front ; border wide, indistinct, 
slightly flattened, very faintly marked off by shallow concentric 
depression. Axis large, convex, more than one-fourth the 
width of the pygidium at front end and extending more than 
half its length, sub-conical in shape, decreasing in width at 
first rather rapidly to behind its middle, then becoming sub- 
cylindrical and having a blunt, rounded, somewhat swollen but 
indefinite posterior end descending suddenly to a short, acutely- 
pointed, triangular, post-axial piece not clearly marked off 
from the axis, but well-defined on each side by convergent 
narrow continuations of the axial furrows which are slightly 
arched inwards and meet at the concentric depression inside the 
border. Axis with two complete distinct rings at its front 
end, corresponding with the two pairs of pleurae on the lateral 
lobes, and followed by 6 or 7 narrow, indistinct, somewhat 
undulating rings, chiefly indicated by transverse rows of 
tubercles. 
Lateral lobes gently convex, arched down on each side, 
bearing two pairs of complete furrowed pleurae. First pleura 
slightly increasing in width outwards, but with nearly parallel 
edges and terminating abruptly on pygidial margin with truncate 
end slightly recurved and pointed at tip, but not projecting ; 
surface with median furrow extending about four-fifths the 
length of pleura ; fulcrum weak, situated at more than one- 
third its length. Second pleura widening more rapidly out- 
wards, but with similarly truncate end ; base about half the 
width of outer end ; median furrow about two-thirds the length 
of pleura, rather sinuous, parallel to posterior edge. Rest of 
surface of lateral lobes without furrows, forming a sub- 
triangular area on each side of the axis and post-axial 
