218 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



head segment is nearly semi-circular, rather more than twice as 

 broad as long, and almost flat. Anterior outline rather regularly 

 curved. The external posterior angles pointed and acute. The 

 concave-convex outline of the posterior margin of each cheek is 

 interrupted by an angular tooth-like projection. 



The Glabella is slightly raised posteriorly, depressed anteriorly. 

 Broadest in front and narrowest at the second furrow at about a 

 quarter the length of the glabella from the base — outline concave 

 laterally to about 2 millemetres from the anterior margin, when it 

 becomes slightly convex. Separated from the lateral portions, 

 or cheeks, by a sinus 1 millemetre broad f millemetre deep to 

 about 2 millemetres from the anterior margin, after this the 

 separation becomes gradually fainter and hardly perceptible at 

 the very front. 



There are four furrows on its surface counting from the base, 



the first entire, the second nearly so, the third and fourth arched to 



about J of the width of the Glabella, and more deeply marked at 

 their inner termination. 



Surface of Glabella covered with concentric folds, the edges of 

 which are about | a millemetre apart. 



The cheeks subtriangular, the inner and posterior margins of 

 nearly equal length. The anterior longer. The eyes are sessile 

 and somewhat reniform. Rather more prominent at the anterior 

 third, and slightly raised above the other parts of the cheek. Facets 

 not so large as those of Phacops. The spaces between the eyes 

 and exterior margins of the cheek, occupied by three curved 

 depressions radiating from the front, and by intervening slight 

 elevations. The sinus and ridge nearest the eye being more 

 curved and sharply defined than the others. 



Three curved slight ridges concave exteriorly and radiating 

 from the anterior corner extend from the inner margfin of the 

 cheek to the eye. The surface is covered with small folds, 

 some being paralled to the anterior edge, and forming a 

 border about 2 millemetres in width, others form a narrow border 

 to part of the posterior margins, while those in the intervening 

 space radiating, follow somewhat the outline of the eye. One 



