242 TRANSACTIONS OF THE [may 18, 
Although the pygidium of our species and that of I. sculptus 
are alike, the head shields are quite different, and the number of 
thoracic joints differs. 
MicRopISscUS PULCHELLUS, Hartt. Plate xvii., fig. 8 a to f. 
Microdiscus punctatus (Salter) Whiteaves. Am. Jour. Sci., 3 
ser., vol. Xvi., p. 225. 
Microdiscus pulchellus, Hartt, Ms. in List to Sir J. W. 
Dawson. 
Microdiscus punctatus, Walcott, U. S. Geol. Surv., Bull. 10, 
p. 24, pl. ii., figs. 1 a to e. 
Microdiscus punctatus var. pulchellus, Trans. Roy. Soc. Can., 
vol. iii., pt. iv., p. 74, pl. vii., figs. 12 a, b and c. 
Description (by Mr. C. D. Walcott).—‘ Head semi-elliptical in 
outline, rather strongly convex, and bordered on the front and 
sides by a depressed furrow and raised rim, the furrow contain- 
ing numerous short furrows perpendicular to the margin, as in 
M Dawsoni, but not as strongly marked. The posterior border 
is strong back of the cheeks, and has the furrow continuing 
from the sides; a very narrow rim extends back of the glabella ; 
eyes and facial sutures entirely absent. 
“Glabella elongate conical, extending backward in a strong 
spine, as long as the glabella in medium-sized specimens, and 
nearly as broad at the base. In some examples the spine is 
shorter and smaller. The glabella rises above the level of the 
cheeks, and is about three-fifths of the length of the head, bor- 
dered by strong dorsal furrows that are connected in front by a 
straight furrow with the depressed groove within the anterior 
marginal border, perceptibly marked by two pairs of oblique 
glabellar furrows in some examples. Cheeks convex, prominent, 
strongly defined by the dorsal and marginal furrows. 
“Thorax unknown.” [see below. } 
“The pygidium, associated with the head of this species in 
great numbers, has the same general outline as the head. The 
narrow, margined rim is well defined all around, widest at the 
sides; anterior marginal furrow very distinct; median lobe 
elongate conical, extending back nearly to the marginal groove ; 
nine anchylosed segments are indicated by eight rather strong, 
transverse furrows; lateral lobes strongly convex, no furrow 
appearing back of the anterior marginal groove.” 
Sculpture.— Surface finely punctate, the punctz being rather 
large as compared with the depth. 
Size.—Dimensions of a rather broad head. Length, 3.5 mm. 
(also 44 mm.). Pygidium, length, 3.75 mm. (also 44 mm.), 
