ON SOME NEW TRILOBITES FROM CANADIAN ROCKS. 237 



the centre, but becoming fainter where it joins the facial suture, a 

 little above the eyes. The anterior portion of the glabella is altogether 

 undefined. The eyes appear to be of the usual Asaphus type ; they 

 are somewhat widely apart ; the breadth between their central points, 

 to the entire breadth of the head-shield across them, is as 5 to 

 9. Except at the striated limb, the whole surface of the head- 

 shield is finely punctured. 



Thorax with eight segments ; division line between the axis of each 

 segment and its pleurse not very sharply defined. There are no inter- 

 mediate V-shaped furrows, as in A. Canadensis. The pleurse curve 

 upwards at their slightly rounded extremities ; they are furrowed to 

 about half their length from the axis, and then crossed by a curvilinear 

 ridge, beyond which the upper portions are delicately striated. The 

 axis and the side lobes (in the transverse measurement of the trilo- 

 bite) are of equal breadth. The middle segments of the axis are 

 slightly broader than the upper and lower, segments. The surface is 

 very delicately punctured. The pygidium closely resembles that of 

 A. Canadensis. In the axis there are from twelve to fourteen seg- 

 ment markings, with a similar number on each side lobe. There are 

 no secondary furrows. The striae on the limb are largely developed. 

 Hypostoma, ^c, unknown. The two nearly perfect specimens and the 

 various fragments of this species that I have examined, belong to indi- 

 viduals of comparatively large size. Of the perfect specimens, one is 

 nearly five inches in length (= 127 millimetres), and the other exactly 

 six inches (= 152.4 mill.) 



Specific Biferences. Asaphus Halli, on accoimt of its rounded 

 genal angles, need only be compared with the follovring species : A. 

 platycephalus, Stokes (Is. gigas, Dekay, &c.) ; A. expansus, Linn. ; 

 A. IfBviceps, Dalman ; A. Barrandei, de Verneuil ; and A. {Is.) affinis, 

 McCoy, the latter species being made to include Portlock's Is. gigas. 

 Is. planus, and Is. Powisii. All the other well recognised species of 

 Asaphus are horned forms. 



The new species differs from A. platycephalus, more especially by 

 its divided glabella, and by the presence of furrows on its pygidium. 



It differs from A. expansus and A. Icsviceps, by the form of the 

 glabella, the angular junction of the branches of the facial suture, and 

 the segment-markings on the side lobes of the pygidium. The latter 

 character distinguishes it also from A. affinis. 



It differs from A. laticostatus, Green — of which species the genal 



