3o8 NORTH AMERICAN INDEX FOSSILS. 



Niagaran of New York and Ontario. 



136. A. occidentalis (Hall). (Fig. i62i,a.) Siluric. 

 Pygidium with the two lateral margins nearly parallel. Differs 



from A. holtoni in having the pleural segments of the pygidium 

 more elongate and directed more nearly in a posterior direction. 

 Niagaran of Indiana, Illinois and Tennessee. 



137. A. nereus (Hall). Siluric. 

 Differs mainly from A. holtoni in that the post-axial lobe of the 



pygidium has a rounded outHne, with a small median notch. 

 Niagaran of New York and Arkansas. 



LII. Amphilichas Raymond. (Platymetopus Angelin in part.) 



Glabella with a large median and a pair of large side lobes, all 

 subquadrate, very slightly expanding anteriorly, and extending 

 posteriorly to the neck furrow ; occipital lobes absent. Pygidium 

 broad and flat, with three pairs of grooved pleura, each ending in 

 a broad, backward pointing lobe. Ordovicic-Devonic. 



138. A. minganensis (Billings). (Fig. 1619.) Ordovicic. 

 Small (length of cephalon 14 mm., width of base of cranidium 



22 mm. ) . Cephalon very convex, bent sharply downward in front ; 

 bounded by a flat border. Median lobe of glabella nearly rectan- 

 gular posteriorly, expanding rapidly anteriorly to the middle ; neck 

 ring broad, flat. Pygidium with strongly elevated, but rapidly 

 tapering axis; each side lobe consisting of three grooved pleura, 

 curving so as to point directly backward, and each ending in a free 

 point. (Type of genus.) 



Chazy of Vermont, New York and Quebec. 



139. A. trentonensis (Conrad). Ordovicic. 

 Cephalon nearly semicircular, very convex, the curve along the 



median line of the glabella from anterior to posterior margins 

 being nearly a semicircle. Median lobe of glabella shaped like an 

 hour-glass; lateral lobes almost as high as the median. Width of 

 cranidium 35 or 40 mm. 



Trenton of New York, New Jersey, Pennsylvania, Ohio, etc. 



140. A. pustulosus (Hall). Devonic. 

 Median lobe of glabella extremely elevated, standing out beyond 



and above the side lobes, its length and greatest width about equal ; 



