166 THE ROYAL SOCIETY OF CANADA 



is associated at New Campbellton with abundant Anthracomya in a 

 series of strata which present strong evidence of freshwater deposition. 



Subclass Merostomata 



Genus Schistaspis 



Schistaspis (o-xio't'os cloven; àcrTrts shield) — Cephalic shield rela- 

 tively large, hemispherical, smooth, with no distinct prominences 

 or glabellar region. Paired median simple eyes doubtfully present 

 near the anterior margin. Head shield articulated behind with a 

 post-cephalic shield whose wing-like expansions are directed outwards 

 and backwards. Abdominal free segments 8 (?) in number, non- 

 trilobate, with spine-like posteriorly directed epimeral projections. 

 The first seven abdominal segments are single. The last abdominal 

 segment is anchylosed to a small hemispherical tail plate which doubt- 

 fully bore a telson spine in articulation with it. 



Schistaspis hretonenis n. s,p. 



Description: Length, exclusive of possible telson spine, 27 mm.; 

 maximum width 12.6 mm. Cephalic shield large, with hemispherical 

 outer border, and concave, evenly curved posterior border. Genal 

 angles acute but scarcely prolonged into a spine. Lateral margin 

 with a narrow raised border which disappears, or is folded beneath, 

 at the extreme front. Although the shield is crushed and somewhat 

 fractured, there is no evidence of a raised glabellar region, nor could 

 the definite presence of compound eyes be detected on the dorsal 

 surface. Medially, however, and situated 1.1 mm. from the front 

 margin there is a minute circular mound about 1/5 mm. in diameter 

 which doubtfully may represent one of a pair of simple eyes. It lies 

 a little to the left of the median line and the corresponding position 

 to the right is ibscured by a bit of matrix. 



Behind the cephalic buckler and free from it, there is a crescentic 

 shield whose anterior convex margin follows the contour of the shield 

 in front. The lateral angles are acute but blunter than the cephalic 

 genal angles. They lie about opposite the fourth abdominal segment. 

 The posterior margin of this thoracic shield is triangular, the two 

 straight edges enclosing in one specimen an angle of 116°, in the other 

 an angle of 103°. 



The first two visible abdominal segments are partly covered 

 by overlap of the crescentic shield. The succeeding five segments 

 are simple and free, with straight axial border in the frontal region of 

 the abdomen but becoming arched in the posterior region. The epi- 



