244 TRANSACTIONS OF THE [may 18, 
associated with it, is partly shown by immature tests that have 
been observed. It acquired generic characters at a very early 
stage so far as the head shield is concerned, but the pygidium 
took a longer time. The Protaspis (slightly over $ mm. in 
length) is remarkable for the equal spacing of the somites al- 
most from the first, causing the first somite to be smaller, 
and the first furrow further forward than usual; while the 
cephalic portion of the axis is visibly segmented, the caudal is 
not, and the line of suture between the two shields is scarcely 
indicated; the rachis almost touches a faintly defined rim at the 
back of the shield. In the } mm. stage of the head shield the 
olabella is already near the normal form in the adult, but ex- 
tends farther forward, and the furrow in front is short and 
deeply impressed, as in the young of WM. Dawsoni and the adult 
of M. Schucherti; there is a slender occipital spine elevated at 
an angle from the plane of the head shield as in the adult. 
When the head shield is 1 mm. long the crenulation on the in-. 
terior of the front rim of this shield becomes visible, and very 
short genal spines are added to the posterior angles. 
When the pygidium was $ mm. long it had three lobes in the 
rachis and one rib marked off by a faint furrow at the front of 
the lateral lobes; this furrow is distinct only in the middle of its 
length; at this stage the shield is much flatter and wider than 
the adult and is bordered by a broad rim, within which is a 
broad rounded furrow. The # mm. shield does not differ much 
in form, but has four rings in the rachis, and the rib at the front 
of each cheek is more distinctly marked. In the 1} mm. stage 
there are seven lobes to the rachis and only a faint trace of the 
rib on the front of the side lobe. In the 2 mm. stage there are 
seven strong lobes and three faint lobes on the rachis, and no 
trace of the rib on the side lobe, so that at this stage the pygid- 
ium has nearly assumed the aspect of the adult shield. 
Horizon and Locality.—All parts of the St. John Basin, in the 
beds carrying the Abenacus Sub-fauna Div. 1 d*. Also in 
Kennebecases and Long Reach Basins at the same horizon. 
MIcRopISCUS PUNCTATUS, Salter. 
Microdiscus punctatus, Salter, Quart. Jour. Geol. Soc. vol. xx., 
no. 19, p: 23%, pl. vili., fig. 11. 
c.f. Microdiscus eucentrus, Linrs. De Under Paradoxideslag- 
-ren vid Andrarum, Stockholm, 1883, p. 30, tab. 4, figs. 19 and 20. 
J. W. Salter’s description of this species is as follows: ‘ Head 
-without eyes or facial suture; margined, the glabella and side 
lobes very prominent, punctate. An enormous nuchal spine. 
