494 
SILURIAN TRILOBITES, 
genus; the number of vertical rows of lenses in each eye is 
seventeen, and the greatest number of lenses in a row is 
five, and this number only in a few rows, the other rows having 
four, three, and two; lenses prominent and not closely packed, 
cups proportionately small, attachment processes visible, cornea 
present as partitions between the oblique rows; as far as we 
have been able to observe, the number of lenses in each eye is 73. 
Thorax — Length about equal to width; axis very prominent and 
semitubular, width throughout almost the same, and equal to that 
of the side lobes; fore rings arched forward, outer ends strongly 
nodular; lateral lobes horizontal between the axial grooves and 
the fulcra; at fulcra deflected at an angle of 65°-70°, width of 
horizontal portion about two-thirds that of the deflected portion; 
pleural furrows deep, vanishing about midway between fulcra ends 
in decorticated specimens; pleurae recurved, facets large and 
procurved, anterior ridges triangular, posterior ones robust and 
merging into the facets. 
Pygidium. — About twice as wide as long, subtriangular, with 
a slight transverse central arch ; axis conspicuous, slightly 
depressed between the side lobes, eight rings present; anterior 
ones intensely arched with a forward inclination, posteriorly 
diminishing in this respect until the terminal piece almost merges 
into the border, posterior width a little less than half of the 
anterior width; six to seven very distinct pleurae on each side, 
very convex, steeply depressed at the sides; pleural furrows deep 
and wide, terminating at the borders; interpleural sutures distinct; 
axial furrows distinct; the whole surface of the decorticated 
specimens shows indication of strong granulation. 
Obs. — Owing to the great tumidity and rugosity of the glabella, 
the deep slit-like character of the glabella grooves (overhung in 
the case of the first pair by the frontal lobes) in the large speci- 
mens of this form, we were disposed to make a separate species 
of this type; but after an inspection of a large number of speci- 
mens we conclude that this greater tumidity, (fee, results from age. 
We have not seen a complete thorax nor the latter with a 
pygidium attached. 
