36 BULLETIN OF THE 
The pygidium is of an oval form, and is about 5mm. broad and 4.3 mm. 
long. The middle lobe is strongly divided from the side lobes by grooves. It 
is very convex, and is also curved antero-posteriorly, giving the pygidium a 
strongly convex outline from front to rear as well as from side to side. It is 
divided into nine or ten segments ; along the median line is a series of tuber- 
cles, very distinct on the anterior segments, diminishing in size near the poste- 
rior extremity. The sides show no traces of segmentation. They are connected 
posteriorly by a narrow ridge similar to that connecting the cheeks. The rim 
is sharp and distinct, being well defined by a furrow which lies between it and 
the side lobes. The specimens are usually of the size above noted, but one al- 
most entire pygidium found at locality No. 2 must, when perfect, have been at 
least 8 mm. long. 
Locality and position. — Stations No. 2 and 3, North Attleborough, Mass., 
Cambrian, thirty specimens. 
20. Microdiscus lobatus, Hall. 
Plate Il. Fig. 13. 
Head minute, 2.2mm. long. The glabella is cut transversely by two fur- 
rows, giving rise to three lobes, of which the anterior one is considerably larger 
than the rest. From the occipital ring to the first lobe the glabella grows 
narrower. The first lobe itself is again larger. The occipital groove is also 
well marked and the occipital ring has the effect of another lobe to the gla- 
bella. The grooves separating the glabella from the cheeks are deep and dis- 
tinct. The cheeks are prominent and strongly convex, bordered distinctly by 
the deep continuation of the occipital furrow. Anteriorly the border is rather 
broad, becoming narrower along the sides. A moderate groove defines the in- 
terior of this border anteriorly ; it decreases much in breadth along the sides. 
Locality and position. — Station No. 2, North Attleborough, Mass., Cam- 
brian, one specimen. 
21. Paradoxides Walcotti, sp. n. 
Plate II, Fig, 12. 
A single specimen was found showing the under side of the integument which 
covered the head, 2.8mm. long, and 3.8mm. broad. The cheeks are in posi- 
tion, and the facial suture is barely indicated by a faint line running from the 
anterior extremity of the palpebral lobe forward, bending at first a little out- 
ward, then more rapidly inward near the margin, which it cuts; posterior to 
the palpebral lobe it almost immediately cuts the margin in a slight outward 
curve. The outline of the head forms a curve, which would be semicircular 
were it not for its disproportionate breadth. There are faint indications of a 
spine at the postero-lateral extremities. The glabella is broad in front, the 
posterior half with incurved sides, narrowing to half its anterior width. The 
occipital furrow is distinct, and the occipital ring has a distinct tubercle at 
