[MatTHEW] ORDOVICIAN SYSTEM ON THE ATLANTIC COAST 269 
fifth rib is obscurely shown; the furrows of the side lobes are straight 
and those toward the back are directed more and more backward, 
Sculpture.—This consists of a fine granulation invisible to the naked 
eye. 
Size.—Middle piece of the head—Length 10 mm. Width at the front 
11 mm., at the back 15 mm. Pygidium length exclusive of the spine 
9 mm., length of spine 3 mm., width 14 mm. 
Locality.-MeFee’s Point near George River, Cape Breton. 
The material on which the above description is based contains only 
the parts figured, and a large free cheek, which appears to belong to 
another species ; it is similar to the cheek of an Angelina (PI. IT, fig. 6.) 
The rock in which this fossil occurs is distorted by pressure and the 
figures are an average of several examples collected for the distortion. 
Dr. Jules Bergeron has decribed a Megalaspis from the Lower Arenig 
beds of the south of France, whose pygidium is similar to that of our 
species, but of which the head is unknown ; his pygidium, however, is 
more exactly that of a Megalaspis.' 
Mr. Walcott has described a pygidium from the Pogonip group of 
Eureka, Col., Bathyurus congeneris, with a broken spine which is like ours, 
but it lacks the border-fold.’ 
Bathyurus caudatus, Bill., from the G-A beds of the Quebec group in 
Northern Newfoundland, based on a pygidium only, resembles our species 
in the number of segments in the pygidium and in possessing a terminal 
spine, but it has no furrow within the border.’ 
In the fragments of rock which contain the above species are a 
broken head-shield of a trilobite resembling a Homalonotus and the 
massive genal spine above referred to. This may have belonged to a 
species like Bathyurellus formosus, Bill. 

1 Massif Ancien au sud du Plateau Central. p. 340, PI. iv., figs. 3 and 4. 
2 Palæontolgy of Eureka District. PI. viii., figs. 8and 8a. 
3 Paleozoic Fossils. p. 261, fig. 245. 
