TRILOBITA— PROP ARIA. 321 



LXV. Pliomera Angelin. (Amphion Pander.) 

 Cephalon broad, short, with a distinct rim around the margin. 

 Glabella moderately elevated, with two pairs of side furrows and 

 short frontal furrows. Free cheeks small. Thorax with 15 to 19 

 segments, with inflated pleura. Pygidium smaller than the ceph- 

 alon; pleural ribs extended into spines. Ordovicic. 



167. P. canadensis Billings. (Fig. 1634, a-c.) Ordovicic. 

 Spines of pygidium wide and close together and so curved that 



all point directly posteriorly. 



Chazy of Vermont, New York and Quebec. 



LXVI. Sph^rexochus Beyrich. 

 Glabella very convex or globular, with three pairs of lateral fur- 

 rows, the posterior one cutting off subcircular basal lobes. Eyes 

 minutely facetted. Thorax of 10 segments; pleura smooth, 

 convex. Pygidium smaller than cephalon, composed of three 

 segments, free at their ends. Ordovicic and Siluric. 



168. S. parvus Billings. (Fig. 1634, ^.) Ordovicic. 

 Neck segment narrow, with furrow deeply impressed. Fixed 



cheeks small, rounded at genal angles, with a wide border com- 

 pletely surrounding them. 



Chazy of Vermont, New York, Quebec, etc. 



169. S. romingeri Hall. (Fig. 1635.) Siluric. 



mm m. 



Fig. 1635. Sphcerexochtis romingeri. Two views of cephalon, natural size ; 

 pygidium enlarged, X 2. (After Hall, 20th Mus. Report.) 



Much larger than 5". parvus. 



Niagaran of Ohio, Indiana, Illinois, Wisconsin, Arkansas and 

 Tennessee. 



LXVII. Phacops Emmrich. 



Genal angles obtuse or produced into minute spines. Glabella 

 tumid, prominent, widest anteriorly; the two anterior pairs of 



