36 
MUSEUM BULLETIN No. 31. 
These characteristics might seem merely the accompaniments 
of the greater size attained' by the specimens, but that such is not the 
case is shown by the fact that there are specimens of C. dentatus 
in Canada which are smaller than the large specimens of C. pleur- 
exanthemus from Trenton Falls. And, furthermore, series of speci- 
mens from Trenton Falls show that there is no backward movement 
of the eye or increase in the length of the genal spines with increase 
of size. 
It is rather peculiar that the only good figure ascribed by the 
earlier writers to Ceraurus pleurexanthemus should prove to belong 
to this species. The illustration referred to is the one given by Bill- 
ings in the Geology of Canada, 1863. The Victoria Museum does 
not contain any specimen as perfect as is indicated by this figure, 
and it is, very probably, a composite illustration. The general form, 
the cephalon, and pygidium appear to have been drawn from speci- 
men Mo. 1775, which was selected as the holotype of Ceraurus 
dentatus , whereas the thorax and ornamentation were apparently 
drawn from specimen Mo. 1769. The sharp pustules on the posterior 
border of the cephalon especially are very like those on that individual. 
The figure is less than half the size of Mo. 1775, but is almost exactly 
one-half the size of a third specimen. No. 1769b. 
Another well-known example of this species is the large specimen 
figured by Hall on Plate 66 of the Palaeontology of Mew York, 1. 
This specimen, said by Hall to have come from “ near Cincinnati, 
Ohio,” is entirely unlike any which has been found in that vicinity 
since, and is very similar to those found in Mew York and Canada. An 
examination of this individual in the American Museum of Natural 
History, Mew York, shows that the lithology is very unlike the yellow- 
weathering rock of the Cincinnatian region, and, moreover, it is 
labelled as coming from Middleville, M.Y. 
This species contains the largest specimens of Oemurus now 
known. The largest is in the Victoria Museum and was collected by 
the late H. G. Vennor at Belleville, Ont. It must have been, when 
complete, over 160 mm . long and 85 mm. wide — a veritable giant, 
when compared with the average specimen of Oemurus pleurexan- 
thevms from Trenton Falls, being nearly double the length of the 
largest found there. The spines on the pygidium grow to great 
length. Those on the type, which is 84 mm. in length, are 27 mm. 
long, and several had longer ones. The spines on a pygidium collected 
by the writer near the base of the Trenton at Healy falls, Trent river, 
Ont., are 38 mm. long. 
Measurements. The holotype is 84 mm, long, 60 mm. wide at 
the genal angles, the cephalon is 24 mm. long, the glabella 17*5 mm. 
