57 
Principal Dmcson — On Neic Palceozoic Crustacea. 
It is associated witli shells of Naiadites carbonarius and N. elongatus 
( Anthracomya of Salter) and with cara- 
paces of Cythere and Bairdia. 
The specimen is a flattened carapace, 
without any of the other parts. Its 
length, without the rostrum, is 0-9 inch. 
The rostrum projects 0 25 inch. The 
extreme breadth is 0-85 inch. The 
surface is smooth at the sides, but pa- 
pillose in the median portion. As com- 
pared with the published figures and 
descriptions of P. dubius, its distinctive 
characters appear to be : — 1. The shorter 
rostrum and larger spines at the anterior 
angles. 2. The reduction of the denta- 
tions on the anterior part of the sides to 
five in number. 3. The presence of two 
strong spines in front of the cervical 
groove at each side of the base of the 
rostrum, and parallel to it, and rather 
less than half-way between it and the 
lateral margins. Whether the dorsal 
ridge extended to the posterior margin 
cannot be seen, as this part of the crust 
is imperfect. In other respects it re- 
sembles the British species, and may be 
merely one of its vaiietal forms. 
Big. 2. 1 Homalonotns Dawsoni, Hall. 
This species was described by Prof. Hall in the Canadian 
Naturalist in 1860, from specimens of the pygidium and portions of 
the body segments, collected at Arisaig, in Nova Scotia. The 
cephalic shield was afterwards found at the same place, and was 
described and figured by Dr. Dawson, in “ Acadian Geology,” second 
edition, 1868. The present specimen, showing the entire length of 
the body, with the exception of a small part of the posterior 
extremity, was found by Mr. D. Fraser, in the Upper Silurian slates 
of the East River of Pictou, Nova Scotia. 
The specimen is a cast of the inner surface of the crust, so that the 
deep transverse furrows are not the margins of the segments, but 
the impressions of their strong internal ridges. The ends of the 
pleuree are bent down abruptly at right angles to the back, giving it 
a very narrow appearance when viewed from above ; but this may 
be partly a result of distortion, in connexion with the slaty cleavage 
which has affected the rock. Still, from the great width of the seg- 
ments, the thorax is of great length, in comparison with the 
cephalic shield and pygidium. and this seems to be one of the 
distinctive characters of the species. The caudal shield, as described 
by Prof. Hall, has, in all, nine annulations ; of which in this specimen 
1 From a Photograph by Ilenderson, reproduced by ‘ Daliastint.’ 
