FOSSILS OF TDE POTSDAM GROUP. 229 



of the dorsal furrows, and reaches to the anterior border. Small triangular 

 occipital nodes are situated one on each side at the base of the glabella. 

 Entire shield margined by a flattened border of moderate width. Thoracic 

 segments unknown. 



The caudal shield associated Avith the above in the same fragments of 

 rock, and in equal numbers, is shorter in proportion to its width, being more 

 regularly rounded, and is margined by a similar flattened border, which is 

 projected in form of a short, spine-like process on each side, about two- 

 thirds of the length from the anterior border. Surface strongly convex and 

 trilobate in the anterior half, the dorsal furrows being directed gently inward 

 for half their length, and then suddenly deflected outward with a slight 

 curvature, becoming obsolete a little behind the middle of the length. An 

 elongated, angular node marks the axial lobe near its anterior margin. Sur- 

 ftice of both shields smooth under an ordinary magnifying power. Length 

 of the larger specimens about one-seventh of an inch. 



Formation and locality.— li\ blackish limestone of the Potsdam group, 

 White Pine. Collected by A. J. Brown, esq. 



Agnostus Neon u. sp. 



PKite I, figs. t'G-aT. 



Cephalic shield short, subparaboloid, three-fourths as long as wide, 

 highly convex; sides nearly straight for half its length from the base, and 

 gradually rounding in front; anterior margin broadly rounded, being almost 

 straight in the middle. Glabella rather more than two-thirds the length of 

 the shield, and less than one-third as wide at its base, conical throughout, 

 more rapidly tapering near the anterior end; anterior third distinctly sepa- 

 rated by a transverse furrow. Dorsal furrows well marked, scarcely con- 

 tinued in front of the glabella; occipital nodes large, rounded-triangular. 

 Lateral lobes of the head convex, margined in front and on the sides to just 

 behind the middle of the length by a narrow, flattened border, which 

 gradually becomes obsolete before reaching the posterior line of the head. 

 Thoracic segments unknown. 



Caudal shield of similar form to the cephalic shield, but entirely mar- 

 gined by a flattened border of nearly twice the width of that of the head, 



