ADDITIONAL NOTES ON THE CAMBRIAN OF CAPE BRETON. 
415 
The genal spines are not as short as Salter’s description indicates, 
for the points are opposite the fourth segment of the throax ; the 
length of the movable cheek and spine, behind the facial suture, is just 
equal in length to the part of the latter behind the eyelobe. 
The eyelobes are variable in position ; in the type figured they are 
just half way between the front and back of the shield ; in examples 
of the narrow form they are, proportionately, further back ; and in 
both forms the width of the middle piece in front is considerably less 
than at the eyelobes. 
In the broad form, the headshield, thorax and pygidium are each 
of about equal length ; others have the pygidium shorter than the 
thorax by the width of one joint. In the narrow form examples occur 
in which the pygidium is longer than the thorax. The pygidium has 
more numerous somites than A. Homfrayi as figured by Salter.* From 
A. affinis McCoy (Ibid) it differs in having the middle piece narrower 
in front, and the glabella and axis of the pygidium more markedly 
elevated. 
Young individuals have the pygidium proportionately shorter and 
wider ; one of about 15 mm. in length has a pygidium equal in length 
to only six rings of the thorax. The thoracic ring is narrow, for one 
is equal in length to the breadth five rings. 
Hypostome. 
This for A. Homfrayi seems very imperfectly known. A good 
example of the Cape Breton variety has the following characters : 
Hyyosiome 16x17 mm. main lobe 11 x 11. No anterior wing or 
doubleur attachment was observed. 
Nearly circular, though wider towards the back than the front. 
It has a moderately arched oval body, with a broad convex border, wider 
towards the back. The main body of the hypostome is divided by a 
pair of diagonal furrows that impress each outward third about two- 
thirds from the front. Immediately behind these furrows are the 
maculiv, sharp, narrow ridges, raised above the general level of the 
hypostome ; no ocular facets are visible, but there are several small, 
obscure pits along the ridge. The macula of the hypostome is opposite 
the eyelobe of the cephalic shield, but is nearer the axial line of the 
body. The furrow within the border is depressed at the back and 
Monograph British Trilobites, p. 165, pi. 24, figs. 6-12. 
