56 Annals of the Carnegie Museum. 



On the specimen here figured the length of the pygidium is only .64 of 

 the width, and the axial lobe of the thorax is narrow for an Isotelus, being 

 only .42 of the total width insti^ad of .50 as in /. gigas. 



Fig. 3. Isotelus maximus Locke. Photograph of a specimen in the Carnegie 

 Museum, to show long genal spines and rounded pygidium. 



Isotelus sp. 

 Plate XV, figure 3. 



Two specimens obtained by Mr. Narraway at Mechanicsville differ 

 from the typical form of Isotelus gigas in having nearly semicircular 

 pygidia, relatively narrower thoracic axes, and smaller eyes. 



The larger specimen retains the cranidium, seven thoracic segments, 

 and the pygidium. The cranidium is smooth, without glabellar furrows. 

 The dorsal furrows are shallow and extend a little ahead of the eyes. 

 Palpebral lobes small, a little further forward than in specimens of 

 Isotelus gigas of this size. 



