218 TRANSACTIONS OF THE [may 11, 
lobe situated in the angle between the cheek lobe and the gla- 
bella. These little lobes [basal lobes] are about one-quarter of 
the size of the anterior glabellar lobe ; cheeks of the same width 
throughout, and uniting in front of the glabella, being bounded 
by the two concentric grooves above mentioned. Posteriorly 
they are rounded ; in width they are rather greater than the gla- 
bella. They are convex, more elevated along their inner mar- 
gin, but sloping outward roundly and evenly. Glabella with its 
lobes project considerably beyond the posterior margin. Sur- 
face smooth. 
‘‘Pygidium of this species (7) of about the same outline as 
the cephalic shield. The posterior and lateral margins have 
a slight, raised border, separated from the lateral lobes by a 
shallow but well marked groove, running parallel to the margin. 
This groove widens at the point where it bends to go forward 
along the sides in such a way as to encroach on and thin out the 
marginal fold, and just before reaching the anterior margin it _ 
narrows itself from the inner side, so as to cause the lateral 
lobes to widen somewhat anteriorly. These are narrow, flat- 
tened, about half as wide as the middle lobe, narrowing to a 
point just behind the middle lobe, where they do not unite. The 
medial lobe is about five-sixths of the length of the pygidium, 
shield-shaped, flattened, convex, more elev ated than the lateral 
lobe. Its anterior border is slightly concave in the middle. 
The lateral angles are rounded, and the lobe is contracted a 
little anteriorly. It is bounded by two deep and well marked 
furrows, which join one another in the middle of the marginal 
furrow, forming a pointed arch; median lobe projecting farther 
forward than the lateral ones. A little spine is situated on its 
mesial line; about one-fourth of its length from its front, surface 
smooth.” 
Mr. Walcott remarks: ‘After a careful study of all the speci- 
mens in the collection, fifteen in number (Hartt’s collection at 
Cornell University), Iam unable to make ont sufficient differ- 
ence between the form described as A. Acadius and that given 
as A. similis, to establish two species. There is a certain range 
of variation in the specimens, as pointed out by Mr. Hartt, but 
that is so variable and owes its origin so largely to the con- 
ditions of preservation of the various Specimens ‘that it is not 
evident that the two species are typified.” 
After examining much larger collections of the Agnosti of 
Div. 1 ¢ (the horizon of the St. John group from which Prof. 
Hartt’s collections came), than Walcott had under review, I am 
not altogether satisfied with the the above determination, though 
it appears to be the best solution as to the use of Hartt’s names. 
