62 
ways destroy the continuity of the costz, as they cross_ 
its this lobe is slightly convex, one inch and a half 
broad at the top, and so continues to the sixth costa, 
after which it gradually contracts, until at the bot- 
tom it is one-fifth of an inch broad, subsiding insensi- 
bly into a flat membrane-like surfaces its longitudi- 
nal sulci pass one inch farther downwards, and ex- 
panding a little, unite with the coste on each side the © 
posterior edge of the space included by them, being 
dentated. | 
The lateral lobes are quite flat, one inch and a half 
broad anteriorly, and, by gradual prolongation, be- 
come at the fourth costa one inch and four-fifths in 
breadth; this dimension is maintained to the ninth 
articulation, when it slowly decreases to one inch at 
the bottom; the recurvature of the costz is gentle in 
the upper eight, but then decreases rapidly. Their 
extremities, advancing two-fifths and four-fifths of an 
inch into the embedding rock, are falcate with their 
‘raised black edges, and clearly marked points. : 
This trilobite was found by Lieut. Bolton, at Lock- 
port, in the state of New York, in the black, shaly, 
horizontal limestone forming the lower part of the 
ravine by which the Erie canal ascends the parallel 
ridge of Lake Ontario. Dr. Bigsby remarks on this 
locality, “Iam not prepared to assign to this lime- 
stone its exact place in the series of geological for- — 
mations; it is above the saliferous sandstone, and 
therefore more recent than the rocks best known as 
abounding in trilobites.” We have, therefore, in this Od 
instance, another fact, which demonstrates that b ‘ind 3 
