RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 33 
approximately vertical to the axis of the animal, but they are usually 
not absolutely straight, but bend a little forward in mid length. The 
posterior furrows run diagonally inward and connect with the neck 
furrow, as in the genus generally. The eyes are close to the glabella 
and opposite the second pair of glabellar furrows. Free cheeks small, 
pitted, with a smooth, convex rim. Fixed cheeks pitted. Glabella 
granulose. The associated hypostoma is roughly tetragonal, the 
surface with sharp, scattered pustules, and the posterior margin nearly 
straight, without spines at the angles. The furrow around the body 
portion is wide and deep. 
Of the thorax only three segments are known. The axial lobe is 
narrow, the inner part of the pleural lobe is crossed by a narrow 
diagonal furrow which separates two triangular nodes, and there is a 
prominent node at the fulcrum. Beyond the fulcrum the pleuron 
projects as a blade-like spine. 
The pygidium is short, with three pairs of slender spines which are 
oval in section and unfurrowed. The last pair extend further back 
than the ones ahead of them. A median spine is present, but very 
short. The axial lobe is narrow, cone-shaped, with the point backward, 
bearing three rings and a node. The pleural lobes are narrow, and 
show a single short divided rib on either side at the anterior end. 
This species is very much like Cheirurus insignis Beyrich. The 
glabella seems to be a little shorter and wider in the American form, 
and the Bohemian species has the eyes further from the glabella and 
has eyelines. Of the latter, however, the specimens in the M. C. Z. 
show a trace. The hypostoma of the Bohemian form is similar to that 
of the American species, but the posterior margin is somewhat wider 
and more flattened. The pygidia are practically the same, though 
the median spine is a little stronger in Ch. insignis. 
It will be seen from the above description, that if we restrict Chevru- 
rus niagarensis to those forms which Hall first identified with Cheirurus 
insignis, we eliminate both the forms which caused him to change his 
mind about the identification, and propose the new name niagarensis. 
This would seem to vitiate the argument above, but it must be re- 
membered that Hall did not recognize that he was dealing with more 
than one species, and he did not apply the new name to any definite 
specimens. In fact, it would seem that he did not become fully con- 
vinced that a new name was needed till he studied the pygidium from 
Waldron, and if the name niagarensis is not to be interpreted as has 
been done here, it would be almost impossible to decide whether the 
Wisconsin or the Waldron specimens should be selected as the types. 
