175 



Pygidiura large sub-triangular, bordered all around, furnished behind 

 with a sharp spine about one-third of its length. The axis is prominent 

 and has three distinct rings and three obscure ones at the back of these ; 

 each of the front rings is furnished with a small tubercle at the back edge. 

 The side lobes of the pygidium have four costse and sometimes a 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. Young point near George River station, Cape Breton. 



The material on which the above description is based contains only the Compared 

 parts figured, and a large free cheek, which appears to belong to another ^ - r 

 species ; it is similar to the cheek of an Angelina (PI. II., fig. b.). The 

 rock in which 'this fossil occurs is distorted by pressure and the figures are 

 an average of several examples corrected 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. 1 



Mr. Walcott has described a pygidium from the Pogonip group of 

 Eureka, Col., Bathyurus congeneris, with a broken sp ne which is like 

 ours, but it lacks the border-fold. 2 



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." 3 



Since the above description was written, the movable cheek of this Movable 

 species has been obtained. It is long, rather narrow behind, and ter- cheek - 

 minates in a long slender genal spine about half of the length of the 

 cheek. There is a marginal fold which is about half as wide as the inner 

 area of the cheek at the eye-lobe ; at the front it extends into a doubleur 

 that passes beneath the front of the middle piece of the head shield. The 

 inner margin of the cheek is not well preserved in the examples known, 

 but the extension of the sutural line, both in front and behind the eye- 



1 Massif Ancien au sud du Plateau Central, p. 340, PI. iv., figs. 3 and 4. 



2 Palaeontology of Eureka District. PI. viil, figs. 8 and 8. 



3 Palaeozoic Fossils, p. 261, fig. 245. 



