62 



ways destroy the continuity of the costse, as they cross 

 it; 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 surface; its longitudi- 

 nal sulci pass one inch farther downwards, and ex- 

 panding a little, unite with the costas 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 costae 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, " I am 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 

 instance, another fact, which demonstrates that blind 



