Io8 BULLETIN OF THE LABORATORIES 
surface; greatest elevation at one-third the distance from the posterior 
margin, from this point rapidly curving downwards to the posterior 
margin, less rapidly towards the side and anterior portion. 
Movable cheeks broadest at the posterior end of the eyes, with a 
deep-rounded furrow around the base of the eye. In large specimens 
rounded above. The facial suture inclining at an angle of sixty 
degrees to the lateral margin in front and meeting it at an angle behind 
which might be called a right angle, with the vertex rounded. It has 
also quite a sharp edge along its posterior margin, where the cheek 
makes a curve beneath the glabella. Since the angle made by the fa- 
cial suture anterior to the eye corresponds to that made by the suture 
anterior to the palpebral lobe in the glabella, the cheeks are associated 
with this species. Eyes placed almost parallel with the upper part 
of the movable cheeks, lunate, forming about one-third of a circle. 
Lenses minute, about 17 to a millimeter. In the specimen examined 
they were only fairly preserved but there were about 20 in the vertical 
rows and perhaps 125 in the horizontal ones. 
Glabellae, pygidia and movable cheeks so far not found in connec- 
tion. The association of the glabellae and pygidia may be considered 
tolerably certain from the great abundance of both as compared with 
those of I. Daytonensis^ the only other species found here in abundance. 
The association of the movable cheeks with these forms is more con- 
jectural. 
Smallest glabella, 8x10 mm. Ordinary sized specimen, 38 mm. 
broad across the palpebral lobes; 35 mm. across the anterior pits of the 
dorsal furrows. Direct length of glabella from anterior to occipital 
margins, 23 mm.; from anterior margin to a line drawn from the occipital 
margin perpendicular to the plane of the lateral margin, 20 mm.; height, 
14 mm. A few large forms have been found which I refer to this 
species. The largest and most perfect of these is in the collection of 
Ira Crawford. It measures 60 mm. across the palpebral lobes and 
54 mm. in a direct line from the anterior to the occipital margin ; 
height, 30 njm. Smallest pygidium 10x13 mm. Ordinary sized speci- 
men, 29 mm. broad at the antero-lateral margins; 24 mm. from pos- 
terior to articulating margin ; 8 mm. high. A single large pygidmm 
referred here measures 52 mm. in width; 44 mm. in length; 16 mm. 
in height. Movable cheeks, large specimen, length, 31 mm.; 
breadth, 20 mm.; length of eye, 7 mm. Smaller specimens propor- 
tionate. 
