io6 
BULLETIN OF THE LABORATORIES 
IV. ILL.ENUS Madisonianus, Whitfield. 
{Plate XIV, Pigs, i a, b; Figs. 2 a, b.) 
Pygidium paraboloid in outline, its anterior margin arching strongly 
forward in the middle, and its surface very convex. Lateral margin 
spreading, forming a broad shallow furrow around the sides and behind, 
just within the edge; anteriorly this furrow extends up the articulating 
slope or facett of the pygidium, leaving it at about half the distance 
from the top of the anterior margin. Anterior margin with a rounded 
ungrooved edge, its corners just without the lateral furrows deflected 
downwards and forwards. A narrow faint ridge running from the 
posterior edge, half way up the pygidium. Entire surface minutely 
punctate with small pits . i mm. in diameter, these interspersed with 
others of still smaller size. 
Length, 30 mm.; breadth, 38 mm,; height 14 mm.; extension of the 
anterior margin forward beyond a line connecting the antero-lateral 
extremities, 9 mm. At the middle of this line is found the greatest 
elevation of the pygidium. 
Our specimen is le.ss abrupt at the sides than the one figured by 
Whitfield and has a smaller elevation along its posterior portion, but 
the general characters agree very closely with the published description 
and figures of the original. The recurved spreading margin seems to 
distinguish it from I. insignis of Hall, the nearest related species. 
Locality and position. Clinton Group, Huffman’s Quarry. 
Another individual from the Soldiers’ Home Quarries is propor- 
tionately broader, more depressed, less extended anteriorly, and pro- 
vided at the anterior margin with a groove. Otherwise it agrees 
closely with the above form, 
V. Illh^nus ambiguus, sp. n. 
{Plate XIV, Figs. 9 a, b; Figs. \o a, b, c; Fig. ii.) 
Glabella regularly arcuate from front to base ; anterior border with 
the margin neatly rounded. Occipital furrow well defined, with a 
faint upward extension at its middle, barely visible, within which is a 
minute granule, which can readily be recognized on wetting the speci- 
mens. Extending towards the anterior margin from this part is an 
indistinct ridge, which can be recognized only with difficulty, except 
in an occasional specimen where it may become moderately distinct. 
