10 Prof. E. J. Chapman on new Trilobites from Canadian Rocks. 



the possession of M. de Verncuil, but unnamed and unfigured, 

 with which our species may very possibly agree ; only the caudal 

 shield of this specimen would appear to possess no lateral seg- 

 mentation, and to have scarcely a defined axis, as M. Barrande 

 refers it to the platycephalus or gigas type*. His statement 

 respecting it is as follows : — w Nous avons vu recemment, dans 

 la belle collection de notre ami M. de Verneuil, un Asaphus des 

 litats -Unis, qui, portant k Tangle genal une pointe longue et 

 grele, constitue une espece tres distincte d'As. (Is.) gigas. Mal- 

 heureusement, nous ne savons quel est le nom specifique qui lui 

 a ete donne par les savans Americains. Ce Trilobite se rangerait 

 dans le groupe de A. gigas, d'apres les souvenirs qui nous restent 

 de sa conformation." 



§ 2. Description of Asaphus Canadensis. — This description is 

 based on what is probably the long or male form. 



General outline a broad oval. Vertical to transverse diameter 

 nearly as 3:2. Relative lengths of head-shield, thorax, and 

 pygidium, as 1 : 0*88 : 1*1. 



Head-shield obtusely pointed anteriorly, much as in Asaphus 

 platycephalus. Genal angles terminating in sharply-pointed 

 horns of the paradoxides type, extending downwards to about 

 the middle of the body f. Facial suture as shown in the figure; 

 the branches uniting in an obtuse but clearly defined angle 

 above the glabella, nearly at the extreme anterior margin of the 

 head-shield, and terminating at the lower margin, about mid- 

 way between the glabella and the genal angles. Glabella feebly 

 raised, broad, and generally conformable at its upper part to the 

 outline of the facial suture. At its base there occurs a slight 

 but evident neck-furrow. There are no furrows on the glabella 

 itself. Length of glabella to length of head-shield as 0*8 : 1*0. 

 Eyes moderately raised and delicately reticulated, although in 

 most specimens they are more or less destroyed. Breadth be- 

 tween the eyes, to extreme breadth of head-shield across them, 

 as 5 : 11. Whole surface of the head-shield covered with fine 

 punctures, except at the striated limb. 



Thorax with eight segments. Axis well defined; narrow, 

 somewhat broader in the middle than at the ends. Mean breadth 

 of axis to breadth of each side-lobe, as 5 : 6. Pleurse termi- 

 nating in slight points, and curving slightly downwards % ; fur- 



* It is perhaps the Asaphus Iowensis of Dale Owen. 



t In most specimens, as in the figure, the horns extend to the bottom 

 of the fourth thoracic segment ; but in a small specimen obtained quite 

 recently from Whitby, and kindly submitted to us by Mr. J. F. Smith of 

 Toronto, they reach to about the middle of the sixth pair of pleurae. 



X In the horned Asaphidce, and in nearly all the horned Trilobites, the 

 pleura; point downwards ; whilst in the forms with rounded genal angles, 



