416 
HULLKTIN OF THE NATURAL HISTORY SOCIETY. 
bordered by a narrow upturned liange, but there is no emargination, 
nor does the border project backward in a fork. The hypostome is 
liighest in the middle of the main lobe, and the convex border is bent 
down in the middle, where it is broadest. 
Development. — Young, 2 x T^ mm. 
This form is interesting as a connecting link between several genera 
of the AsaphidaL It may be said to antedate the development of the 
generic characters. 
At this stage the carapace had no flattened borders, and the head 
shield especially was strongly bent down in front and at the sides. 
The back of the glabella is very distinctly marked out, and here the 
head-shield is strongly trilobed. About the middle, on the inside 
of the shield, a flaring ridge runs out on each side from the 
glabella, and fades away on the surface of the test, that appears to be 
the back part of the eyelobe. At this stage no movable cheek had 
been detached, but the genal corner of the shield is somewhat ex- 
tended into a short point. There are indications of several somites 
in the head shield ; first the neck ring and posterior marginal fold, 
then a pair of somites indicated by incipient furrows on the sides of 
the glabella, then the ocular segment. 
The thorax, at this stage, possessed two joints, with rounded rings 
and pleune. 
In the pygidium, the neopygidium and protopygidium* are dis- 
tinct ; the former has three rings as strongly marked off as those of 
the thorax, the protopygidium has the same number of obscure somites. 
In this larval form, which in development is close to the unseg' 
mented larva, the outline of the headshield distinctly recalls the adult 
in Illnenus and Dysplanus, but the strongly segmented pygidium has 
an even more generalized meaning. 
Young G X 5 mm. 
This moult already possesses many features of the adult. 
The flattened borders are obvious on both shells, and the head- 
shield is broken up into the three principal pieces. The movable 
cheeks have heavy genal spines, and the course of the suture is function* 
ally that of the adult. The slipping of the cheeks in this example 
has obscured the eyelobe, which, however, appears to be not far from 
* Trans. Roy. Soc. Can. 2nd Ser., vol. iv, sec. iv, p. 145., lines 24, 27. 
