1896. | NEW YORK ACADEMY OF SCIENCES. 219 
It appears strange that while A. fallax and its varieties are by 
far the most common Agnosti of that horizon, Hartt should de- 
scribe only spineless pygidia; these I find comparatively rare at 
this horizon, though they become plentiful in Div. 1 d (whose 
fauna Hartt did not have). And then the description of A. 
similis more nearly accords with that of A. fallax than does 
that of A. Acadicus. 
Size.—Length of each shield, 5 mm.; width, 54 mm. 
Horizon and Locality.—Grey shales of Div. 1 ¢ at St. John, 
Radcliff’s stream, ete. 
Var. DECLIVIS. pl. xv., figs. lla to d. 
Agnostus Acadicus var. declivis, Trans. Roy. Soe., Can. vol. 
iiil., p. 70, pl. viii., figs 6a and b. 
This form is closely allied to A. Acadicus, but presents the 
following differences: It has a narrower border foid and smaller 
basal lobes, the glabella has proportionately a longer anterior 
lobe, and the furrow dividing it from the posterior lobe is di- 
rectly transverse; the posterior lobe is strongly elevated, al- 
most tumid behind, and bears a small round tubercle at the 
middle of its length; in front of the tubercle the lobe slopes 
down rapidly to the cross-furrow. 
Differences of equal import are found to exist between the 
pygidia of the two forms. In var. declivis the rachis is cylindro- 
conical, and there are three minute lobes on each margin near 
the anterior end; in A. Acadicus the rachis is more triangular 
in form, and both the head and tail shields are found of a larger 
size than those of the variety. The marginal fold is not quite 
even, but is interrupted not quite half-way to the back of the 
shield by a small, inconspicuous, knob-like spine. A pair of fur- 
rows just in front of the tubercle on the glabella, and snother 
pair a little behind it, both directed slightly backward, slightly 
indent the sides of the glabella. 
The thorax, of two joints, has three lobes on the axis of each 
joint, the mid-lobe being wider, and the side lobes lower on the 
posterior than on the anterior joint ; the pleura have furrows di- 
rected forward; that on the hinder joint is placed on the front 
and that on the interior joint on the back of the pleura. 
This variety has the head of a Fallax with the tail of a Brevi- 
frons (e. g., A. parvifrons Linrs.). 
Development of the young.—Head shield of ? mm. long has 
no visible basal lobes, but otherwise does not differ much from 
the adult. In a head 14 mm. long these lobes become visi- 
ble, but are very narrow and are confluent with the posterior 
marginal fold. 
