234 ON SOME NEW TRILOBITES FROM CANADIAN ROCKS. 



§3. Specific Differences: — (1.) Asaphus Canadensis differs from 

 A. platycephalus, Stokes (Isotelus gigas, Dekay) ; A, expansus, Linn ; 

 A. Barrandei, de Verneuil ; A. Iceviceps, Dalman ; A. (Is.) affnis, 

 McCoy, (including Is. gigas, Is. planus and Is. Powisii of Portlock) — 

 in having, with other opposing characters, the genal angles of the 

 head-shield extended into horns. 



(2.) It differs from A. tyr annus, Murchison; A. Powisii, Murchison; 

 and A. ingens, Barrande — in having, with other opposing characters, 

 the branches of the facial suture united above the glabella on the up- 

 per surface of the head-shield. 



(3.) It differs from A. nobilis, Barrande — in wanting the curved 

 furrows on the axis of the pygidium, as exhibited by that species ; and 

 also by the greater number of the segment-markings on the side-lobes 

 of its pygidium, as well as by the general outline of the facial suture, 

 mid other characters. 



(4.) It differs from A. extenuatus, Waldheim — by the obtuse out- 

 line of its cephalic shield, and by other marked characters. 



(5.) It differs from A. {Is) laticostatus. Green — the genal angles of 

 which are unknown — by its thorax being nearly of the same length as 

 its head-shield, and by the greater number of segment markings on 

 the side lobes of its pygidium, as well as by other characters. 



(6.) It differs from A. ovatus, Portlock, by the presence of segment 

 markings on the side lobes of its pygidium. I am not acquainted 

 with the head-shield of A. ovatus, and I cannot obtain here a copy of 

 Colonel Portlock' s Report in which the species is figured. 



(7.) It differs from A. angustifrons, Dalman ; and A. frontalis, 

 Dalm. ; by the greater development of its genal points, Dalman's 

 species being placed by him under his subdivision of " Mutici," com- 

 prising the forms with rounded or but slightly pointed genal angles. 

 I am not sufficiently acquainted, however, with these Swedish species 

 to name any other distinguishing characters, and I have no means of 

 procuring here a copy of Dalman's "Palaeden," in which the species 

 are described. 



(8.) It differs from A. lowensis, Dale Owen, by its genal points 

 reaching only to the middle instead of to the end of the thorax ; by 

 its facial suture being pointed, instead of curved, above the glabella ; 

 and by the presence of segment-markings on its pygidium. 



The head-shields of A, grandis, Sars ; A. Fournetti, de Verneuil ; 

 and A. latimarginatus. Hall — are yet unknown. 



