758 THE PALEONTOLOGY OF MINNESOTA. 



[Harplua rutrellum. 



axial length of the shield, anterior extremity narrow and obtuse. Basal lobes very 

 broad and large, together making the glabella considerably broader at the occipital 

 ring than it is long. These lobes are separated from the glabella by short, posteriorly 

 oblique lateral furrows, and from the cheeks by deep grooves which are abrupt and 



Figs. 80, 81. Portion of cephalon of Harpina rutrellum, with sectional outline showing the charac- 

 ter of the doublure. 



ridged on their outer margins. The occipital ring is narrow, elevated and well 

 defined over about one-half the extent of the cheek. Cheeks somewhat flattened 

 above, abruptly deflected to the concave margin. Eyes small, nodiform, distant 

 from the glabella and situated in a transverse line cutting the shield at its center. 

 Surface of convex portion of shield covered with coarse, deep, irregular punctures 

 which are coarsest about the eyes and on the anterior slope of the shield, become 

 finer and more nearly circular about the margin. The glabella is covered with 

 shallow, irregular pits, while the basal lobes and occipital ring are smooth. Doublure 

 flat, its width equalling that of the concave part of the upper surface; thence it is 

 bent upwards at a right angle, its distal portion becoming parallel to the anterior 

 slope of the shield, as in the accompanying figure. The outer surface of the flat 

 area is covered with large and very coarse circular punctae. Length of specimen 

 9 mm.; probable width at base, 16 mm. 



Though there is but a single example of the head, the characters above given 

 are sufficiently distinctive. Whether a second specimen showing only the flat 

 portion of the doublure belongs to the same species it is impossible to decide 

 definitely, though the character of the punctation is essentially similar, and the 

 vertical section shows that the upper surface was concave about the margin. 

 Perhaps the species most closely allied to ours is Prof. Hall's Harpes escanabce* from 

 the Trenton horizon on the Escanaba river. This was based upon the marginal 

 rim of a small cephalon described as being strongly pitted with the punctae arranged 

 along the outer and inner edges of the finer and more abundant perforations in the 

 middle. This agrees with the character of the under surface of the second of our 

 specimens, but not with the upper surface of the first and more typical example. 



Harpina rutrellum may also be compared with H. antiquata Billings, of the Chazy 

 limestone. 



Formation and locality. The cephalon described is from the Galena beds at Cannon Falls, Minn. 

 (Mr. Ulrica's collection); and the fragment of the doublure is from the Trenton at Minneapolis (Museum 

 No. 8420). 



Fotttr and Whitney's Bept. Geology of Lake Superior, p. 211, pi. xxvn, flg. 2rt, 1861. 



