274 G. F. MATTHEW ON THE 
The first type (A), which is also the smallest, is frequently met with, and exhibits a 
considerable variety of forms. From their abundance it is supposed that these pygidia 
pertain to P. eleminicus and its allies. They have a marked sinus at the extremity. I 
figure and describe the principal varieties observed. 
All the pygidia of this type were found at Portland in Div. 1c. 
Type A a (Fig. 16.) 
Nearly orbicular and about as wide as long. 
Axial lobe about one third of the whole length and but slightly raised above the 
general level of the pygidium ; a narrow ring in front is divided by a distinct furrow from 
the semi-circular posterior segment. 
Marginal third —There is a raised crescent-shaped tract behind and higher than the 
axial lobe, and a depressed zone of the pygidium encloses this tract and the axial lobe, The 
marginal zone is slightly convex in the anterior half, but flat behind, where there is a 
marked sinus two thirds as wide as the front of the axial lobe. 
Sculpture —The surface is shining and minutely granular; the granulations are most 
distinct on the front of the elevated tract behind the axial lobe. 
This is the only pygidium found at Saint John (Portland) which has a semi-circular 
axial lobe, and it perhaps belongs to some other species than P. eteminicus. 
Type A b (Fig. 17.) 
Broadly ovate and about one sixth wider than long. 
Axial lobe more than half of the whole length of the pygidium ; ovate-conical, mo- 
derately convex: first ring sharply divided off from the rest of the lobe, and having a 
narrow lunate segment, of about half its length, marked off from the posterior side: a 
second ring is indicated by faint depressions on the axis: the remainder of the lobe has 
two points or faint ridges which are directed forward toward the axial line. 
Marginal third—The inner zone of the marginal area is raised into a strong elevation 
just behind the end of the axial lobe, which elevation in young individuals has the appearance 
of a tubercule. The outer zone is moderately convex in the anterior half and flattened at 
the posterior part, where it is also truncated, or slightly arched inward at the margin. 
Sculpture—The whole surface is shining and minutely granulate or pitted, the most 
distinct pits being on the axial lobe; The posteror quarter of the marginal area is wrinkled, 
and along the sinus at the end are two or three faint, raised lines. 
Type Ac (Fig. 18.) 
Pygidium ovate, and as long as wide. 
Azial lobe half of the whole length of the pygidium ; broad-ovate, moderately convex ; if 
bounding furrow rather faintly marked. One ring faintly indicated. 
Marginal third—The inner zone is but slightly marked off from the outer, and bears a 
sharp eleyated ridge (perhaps due to an accident of preservation) which arches across from 
side to side, around the extremity of the axial lobe. Outer zone as in b, but the sinus 
deeper and about three quarters of the width of the axial lobe. 

