264 PALEONTOLOGY. 



Formation and locality. — In limestones of the age of the Waverly group 

 of the Mississippi Valley, at Ogden and Logan Canons, Wahsatch Range, 

 and Dry Canon, Oquirrh Mountains, Utah. Collected by S. F. Emmons 

 and J. E. Clayton. 



riJOKTUS LOGANENSIS 11. .sp. 

 I'l.ato IV, (i;;. 33. 



The pygidium of a small species differing very materially from the 

 preceding occurs at Logan Canon, associated with that one. The form is 

 more nearly semicircular, being but very slightly paraboloid. The axial 

 lobe is highly convex, rapidly tapering below and terminating abruptly a 

 little within the posterior margin ; anterior end forming fully one-third of 

 the entire width of the shield. Lateral lobes moderately convex, with a 

 slightly thickened, scarcely elevated border of moderate width, on which 

 the ribs become nearly obsolete. Axial lobe marked by nine rounded and 

 distinct annulations, exclusive of the terminal ones ; strong in front and 

 rapidly decreasing in size posteriorly. The ribs of the lateral lobes are ten 

 in number on each side ; simple, highly rounded, and continuing entirely 

 around the posterior margin of the shield, the most posterior ones being 

 very faintly marked. 



This species differs conspicuously from the corresponding parts of 

 P. peroccidens in its shorter form, small number of ribs, and in being desti- 

 tute of the surface ornamentation which characterizes that one. 



Formation and locality. — In limestones of the age of the Waverly group, 

 at Logan Canon, "Wahsatch Range, Utah. Collected by S. F. Emmons, esq. 



