158 



Contributions to Palaeontology. 



This species is comparatively rare: a few individuals occur in 

 some specimens from the Marine mills on the St. Croix river, with 

 large numbers of Conocephalites oweni. It is very distinct from 

 any other, in the depressed flattened area just forward of the gla- 

 bella, and the abrupt elevation and flattened anterior border. 

 There is considerable diversity of expression given to this species, 

 from the greater or less extent of the depressed flattened portion of 

 the limb in front of the glabella, and also from the imperfection of 

 the anterior border of the limb, which sometimes leaves it little 

 wider than the posterior flattened space. 



I have collected the same species on the west side of the St. 

 Croix river, about two miles below the Falls. 



GENUS ARIOKELLTJS ( Barrande). 

 ARIONELLUS BIPUNCTATUS. 

 PLATE II. FIGS. 50 & 51. 



Arionellus bipunctatus : Shumard, Trans. Acad. Sciences of St. Louis, Vol. ii, 



No. 1, p. 101. 



The following is Dr. Shumard' s description of this 

 species : 



" Small, moderately elevated. Glabella convex, conical, 

 " truncated or sometimes very gently arched at apex: 

 " length, excluding the neck-segment, equal to the 

 " width at the base ; sides gently convex ; neck-furrow 

 " straight, moderately deep and well defined ; neck- 

 " segment short, semielliptical, with the sides gently 

 " rounded. Dorsal furrows distinct all around, as 

 "deeply impressed as the neck-furrow, and marked 

 " opposite each angle of the glabella in front with a 

 " minute circular depression. No lateral furrows visible 

 " on any of the specimens under examination. Front 

 " margin rounded, and occupying about one-fourth the 

 " total length of the head. 



" Movable cheeks regularly convex, margined with a nar- 

 " row rounded raised border ; genal angles prolonged 

 " into long slender curved spines. 



