346 Description of several new Trilobites. 
they occur is a ferruginous clay slate, filled with other petrifactions. 
My friend Joun F. Frazer, Esq. informs me that the geological 
structure of Huntingdon and its vicinity, belongs to the classification 
of rocks, called by Professor Rogers, in his annual report as State 
Geologist, the olive slate stratum. ‘This stratum reposes on a coarse 
grained sandstone, full of organic remains, and is thus described in 
the report. 
“The next stratum is a dull olive colored slate, alternating with 
grey argillaceous sandstones. ‘Towards the upper portion some of 
the layers consists of a soft, very yellow slate, which increases as 
we ascend, becoming, in the upper part, the principal variety. It 
alternates with beds which gradually assume a brown and reddish 
tinge, that grows gradually mor e distinct, indicating the gentle passage 
.of this rock into the red argillaceous stratum above it. The inferior 
layers contain occasionally large deposits of a very argillaceous iron 
ore, approximating. in its composition and characters to the argilla- 
ceous jron stone of the coal measures. This stratum abounds also 
in mineral springs, the predominating ingredient of which is sulphu- 
retted hydrogen. It may for convenience sake, be called the olive 
slate stratum.” : 
Crveuzus Collitelus. Green. 
Cauda utrinque in lobis quinque divisa; lobis elongatis, rectis, 
acutis. ‘ 
I have seen the caudal end only of this exceedingly interesting 
trilobite, but it differs so much from the other species described, that 
there is little doubt of its being distinct. There are eleven or twelve 
articulations of the vertebral column, and but five of the costal arches 
of the sides visible in our fragment. The joints of the middle lobe 
of the back are narrower, more numerous, and by no means so prom- 
inent as those of the C. Boothii, and the terminal joint is also much 
smaller. ‘The costal arches or ribs of the sides are remarkably broad, 
and are strongly marked by a deep sulcus running along their infe- 
rior edge ; they commence at the seventh joint of the vertebral col- 
umn. The scollops or leaf-like lobes of the tail are five in number; 
and are remarkably large in proportion to the body of the animal; 
they form a regular continuation of the last five arches of the sides, 
and terminate in free points, without any curvature. A thin rib 
passes from the tip of each lobe through its middle to the sides of 
animal, probably for the purpose of giving strength to the large 
at of the membrane. The body of the animal is broad, 
