120 PALAEONTOLOGY OF OHIO. 



tion of the glabella forward of the dorsal furrows. Palpebral lobe small, 

 pointed, and sharply elevated above the general surface of the head, situ- 

 ated very near the posterior margin. Suture line gently and regularly 

 curving inward for a short distance in front of the eye, and then as 

 gently outward again, giving to the glabella a little greater width an- 

 teriorly than immediately in front of the eye, the junction with the an- 

 terior" margin making no perceptible angle. The direction of the suture 

 line posterior to the eye, and the form of the postero-lateral limb of the 

 glabella, have not been determined. 



The pygidium associated with this form of glabella, and supposed to 

 belong to the same species, is somewhat longer than semicircular in 

 form, the length being a little more than two-thirds as great as the ex- 

 trem.e width. General surface depressed convex, with rather strong de- 

 pressions defining the axial portion on the anterior fourth of the length, 

 but gradually fading away before reaching the middle of the plate. An- 

 terior margin nearly straight, the axial portion slightly' protruding 

 beyond the line of the lateral lobes, which are straight for a little more 

 than half their width, beyond which they are strongly and obliquely 

 truncate. No portion of the thorax has been observed. 



The specimens resemble /. Taurus, Hall, in many of their characters, 

 as the small, pointed, and projecting eyes, placed so far back on the head, 

 and in the trilobation of the caudal plate in its anterior part, but the 

 glabella is very much longer in proportion to the width, as is also the 

 pygidium, and the antero-lateral truncations of the latter are not more 

 than half as large as in that species. The facial sutures of the head also 

 dififer very materially. In that species it is directed from the front of the 

 eye, with a very moderate curvature, inward, meeting the anterior border of 

 the head at a point which gives a width on the margin of but little more 

 than half that immediately in front of the eye, while in this species the 

 breadth near the anterior margin is greater than immediately in front 

 of the eye prominence. The pygidium resembles, slightly, small speci- 

 mens of that of I. imperator. Hall, but is much longer in proportion to 

 its width. 



Formation and locality : In the limestones of the Clinton group, near Dayton, Ohio. 

 Specimens having the same features have been collected from the Niagara group of 

 Wisconsin and Illinois. 



