Silurian Fossils of Canada. Q6 



Phacops Orestes, N, s. 



Fig. 10. — Phacops Orestes, a the eye enlarged. 



Description. — Oval, about one inch and a quarter in length. 

 Head somewhat semicircular or sub-crescentiform, the front con- 

 vex and the posterior margin concave, the angles rather pointed 

 but not produced into spines. Glabella moderately tumid, de- 

 pressed convex on the top abruptly descending to the front margin, 

 separated from the eyes by a narrow deep furrow, the anterior 

 angles spreading out and becoming obsolete in front of the centres 

 of the eves, an indistinct maro-jnal o-roove round the front which 

 does not extend to the cheeks beyond the anterior angles of the 

 glabella. The neck segment is strongly elevated, connected with 

 the main body of the glabella by a narrow convex neck-like 

 rido-e with a small rounded tubercle on each side. All of the 

 glabellar furrows are but slightly impressed ; the two anterior are 

 situated close to the inner front angles of the eyes, their direction 

 forming with the longitudinal axis of the body an angle of 45° ; 

 they slope forward and outward and are short, a little curved and 

 so faintly impressed that they can be seen on very perfect speci- 

 mens only. The middle furrows lie in a line drawn across the 

 head cutting the eyes at points a little less than one fourth of 

 their length from their front angles; in some specimens these 

 two furrows appear to be straight but in others a little curved 

 the Convex side towards the front. The posterior furrows lie a 

 little behind a line drawn throuo-h the centres of the eves. The 

 sides of the glabella are straight or nearly fo from the tv/o neck 

 tubercles to the inner front angles of the eyes when they curve a 

 little outwards and become obsolete on approaching the ill-defined 

 anterior angles (of the glabella) which are situated midway be- 

 tween the eyes and the anterior margin. 



The eyes are very large, sub-semicircular, the lens-bearing sur- 

 face not vertical but above sloping a little inwards, more elevated 

 at the anterior than at the posterior extremity ; lenses about seventy 

 five arranged in vertical rows in general five in each row. Length 



Can. Nat. 5 Vol. V. No. 1. 



