FOSSILS OF TIIK KKOKUK GROUP. 529 



crust is removed, numerous very minute lenses beneath. 

 Cheek sloping off rather abruptly from the eyes to the 

 thickened margin, which does not continue around the 

 front of the glabella; facial sutures cutting the anterior 

 margin in front of the eyes before, and a little outside of 

 them behind. Thorax nearly twice as wide as long, dis- 

 tinctly trilobate; mesial lobe- but moderately prominent, 

 nearly twice as wide as either of the lateral lobes, its eight 

 segments merely rounded, and without furrows. Lateral 

 lobes narrow; pleura? curving moderately downwards at 

 less than half their length out from the axial lobe, but not 

 distinctly geniculated, each provided with a furrow extend- 

 nearly half way out. Pygidium approaching semi-cirular, 

 with the anterior lateral angles obliquely truncated; mesial 

 lobe but slightly wider anteriorly than the lateral ; segments 

 about eleven; lateral lobes with eight or nine segments. 

 Surface finely granular, the granules being most distinct 

 on the glabella, and the segments of the mesial lobe of the 

 thorax. 



This species will be at once distinguished from our P. Portlockii, from 

 the same horizon, by its much broader and less ventricose glabella, and 

 the peculiar tuberculiform eyes of that species, as well as by the broader 

 and less prominent mesial lobe of the pygidium, in the form under con- 

 sideration. 



Locality and position Crawfordsville, Indiana ; Keokuk division of 

 the Lower Carboniferous series. 



