2l6 THE CHICAGO ACADEMY OF SCIENCES. 



downward laterally from the dorsal furrows, the eyes mod- 

 erately protuberant with a rather broad, shallow, rounded, 

 ill-defined furrow beneath them upon the free cheeks. Free 

 cheeks rather large, the posterior limb of the facial suture 

 curving backward and downward from the posterior extremity 

 of the eye, the anterior limb bending downward and forward 

 with a slight concave curve and intersecting the margin almost 

 directly in front of the eyes, it then follows the margin for a 

 short distance towards the front before curving to the ventral 

 side where it continues around the anterior extremity of the 

 cephalon parallel with the margin and joins with the furrow 

 from the opposite side. 



Pygidium semi-ellipitical in outline, strongly convex, 

 greatest convexity near the middle, slightly flattened at the 

 .antero-lateral angles, with no indication of axial furrows or of 

 -a differentiated axis, but usually marked by a slight, median, 

 longitudinal ridge from near the center to the posterior ex- 

 tremity. 



The dimensions of a large and nearly perfect cephalon are: 

 width 76 mm., length 35.5 mm., convexity 47 mm.; the dimen- 

 sions of a pygidium are: length 56 mm., width 54 mm., con- 

 vexity 25 mm. 



Remarks. Specimens have been identified as /. insignis, and 

 their relations discussed by four authors since the species was 

 originally described by Hall. In the original description the 

 character of the strongly marked, elongated dorsal furrows ter- 

 minating in distinct rounded pits is considered as the most char- 

 acteristic feature of the species, and this character is well shown 

 in the specimens from Haw.thorn, where the species occurs in 

 great numbers almost to the exclusion of other members of the 

 .genus. These Hawthorn specimens, however, are constantly 

 more pointed at the front of the cephalon than Hall's illustra- 

 tions would indicate, but none of Hall's figures give a direct 

 vertical view of his specimens, the cephalon being tipped back- 

 ward so that the anterior margin would appear less pointed 

 in the picture than it actually is in the specimen. The pygidia 

 from Hawthorn which gccur associated with the heads in about 

 equal numbers, agree fairly well with the pygidia figured by 

 Hall, but they are usually marked by a longitudinal median 

 ridge which is not shown- by Hall. The original pygidium used 

 by Hall, however, is a small one, which may account 'for the 

 absence of the rib. 



