FAUNA OF THE ST. JOHN GROUP. 275 
- Sculpture.—Appears dull and velvety to the naked eye, but under the lens is seen to be 
minutely granulate: the under side of the pygidium is marked by concentric raised lines, 
which on the posterior part are separated by about the space of half a millimetre, and are 
rudely parallel to the crescent-like ridge on the middle of the pygidium. 
Type À d (Fig. 19.) 
Pygidium rhombic-ovate and about as wide as long. 
Axial lobe lance-ovate in form and three-fifths of the length of the whole pygidium : 
moderately convex in the anterior two thirds, but flattened and scarcely distinguishable 
from the marginal area in the posterior third. Only one ring at the anterior end of the 
axial lobe ; from the back of this ring a narrow, lunate segment is marked off by a light 
furrow extending across the lobe. 
Marginal third is impressed in its anterior part by grooves originating from the ends 
of the furrows bounding the axial ring; the points of these impressions are bent toward 
the axial lobe, but do not reach it extremity: two faint depressions parallel to the outer 
margin, traverse the rest of the marginal area. On the axial line there is a small ovate- 
acuminate plate, which occupies more than half of the space from the point of the axial 
lobe to the posterior extremity of the pygidium. This part of the pygidium is sinuate, 
having a shallow indentation about two thirds as wide as the front of the axial lobe. 
Sculpture—The whole surface is shining and under the lens is minutely tuberculose. 
No raised lines are visible except a few near the posterior margin; these are transverse to 
the length of the pygidium and rudely parallel to each other. 
Length of the forms of this type vary from half an inch to seven-eighth’s of an inch. 
The pygidia of the second group (B), are considerably larger than those above des- 
cribed and were all found in the soft dark grey shale in the upper part of Division 1c. 
They are characterized by a shallow sinus with rounded corners, which is sometimes only 
a slight waving inflection of the posterior margin. The following are the principal va- 
rieties. 
Type B a (Fig. 13.) 
Obcordate and about one-eighth wider than long. 
Axial lobe about two thirds of the length of the whole pygidium ; ovate and somewhat 
longer than wide; moderately convex and distinctly bounded. There is a broad ring in 
front, which with the anterior furrow and articulating front of the pygidium form about 
one third of the whole lobe. There are indications of a second ring of about the same : 
width as the first. 
Marginal third.—The inner zone is flat and without special features, the outer zone is 
moderately convex in the anterior two thirds, flat elsewhere and sinuate at the base; the 
sinus is shallow and about one quarter wider than the front of the axial lobe. 
Sculpture —The axial lobe is smooth and velvety; the marginal area is also smooth, 
but more glossy than the axial lobe. A few faint lines were observed close along the pos- 
