26 



TMs species somewhat resembles A. megistos, Locke, figured in the 

 (Trans. Am. Ass. Geols and Nats. 1853, pi. VI.) But according to that 

 figure the eye of A. megistos is about one-sixth the length of the head ; a 

 line drawn across the head at the mid-length is more than the length of 

 the eye distant from the anterior angles of that organ ; the head is one- 

 ninth longer than the thorax. There are other difierences, but these are 

 the more important. 



This species occurs at English Head ; H. R, Also, at Gamache 

 Bay in Div. 1., A. G. T. C. Weston. 



A. ALACER, n. sp — This species is ovate, broadly rounded at both extre- 

 mities, (pygidium obscurely or not at all trilobed ?) Cheeks without ter- 

 minal spines. Head convex, semi-elliptical or lunate, uniformly rounded 

 in front, gently convex at the sides ; angles acutely rounded ; length, by 

 caUipers, to the width in the proportion of four to seven. Eyes annular, 

 abruptly elevated on the outside, flat or gently convex on the top, scarcely 

 rising so high as the glabellar space between them ; their length is to that 

 of the head in the proportion of three to eight ; their anterior angles reach 

 the mid-length of the head. The rows of lenses, seen under the transpar- 

 ent cornea, cross each other diagonally, both sets being oblique. Thorax 

 distinctly trilobed, axis moderately convex more than one-third the whole 

 width. Pygidium depressed convex, semielliptical ; margin broadly 

 rounded ; length to the width in the proportion of 3| to 6f . Surface ap- 

 parently smooth. 



The specimen is a small rolled up individual, perfect with the exception 

 of the central part of the pygidium where it is worn so that the characters 

 of the axis cannot be made out. 



Fio;. 9. 



Fig. 9. — a, front view of the head of A. alacer ; b, front view of the 

 head of A. platycephalus. 



This species differs from A. notans, in the absence of cheek-spines, in the 

 form of the eyes and also in their elevation. In the former they are so 

 much elevated that viewing the head directly in front, the outline between 

 them is concave ; in the latter sHghtly convex. In this latter respect also 

 it differs from A. platycepJialus. 



It occurs at Charleton Point ; H. R. J. Richardson. 



A. MEGISTOS, Locke. — Fragments of a large trilobite either identical 

 or closely allied to this species occur at numerous localities on the north 



