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 hypostonia 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 Cheiru- 

 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. 



