Prof. E. J. Chapman on new Trilobites from Canadian Rocks. 15 



Thorax with eight segments ; division-line between the axis 

 of each segment and its pleurae not very sharply defined. There 

 are no intermediate V-shaped furrows, as in A. Canadensis. The 

 pleurae 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 Trilobite) are of equal breadth. 

 The middle segments of the axis are slightly broader than the 

 upper and lower segments. The surface is very delicately punc- 

 tured. The pygidium closely resembles that of A. Canadensis. 

 In the axis there are from twelve to fourteen segment-markings, 

 with a similar number on each side-lobe. There are no secondary 

 furrows. The striae on the limb are largely developed. Hypo- 

 stoma, &c, unknown. 



The two nearly perfect specimens and the various fragments 

 of this species that I have examined, belong to individuals of 

 comparatively large size. Of the perfect specimens, one is 

 nearly 5 inches in length (= 127 millimetres), and the other 

 exactly 6 inches ( = 152*4 mill.). 



Specific differences. — Asaphus Halli, on account of its rounded 

 genal angles, need only be compared with the following species : 

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

 Linn.; A. Iceviceps, Dalman; A. Barrandei, De Verneuil; and 

 A. (Is.) affinis, M f Coy, the latter species being made to include 

 Portlock's Is. gigas, Is. planus, and Is. Powisii. All the other 

 well-recognized 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. Iceviceps 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 angles are unknown, — by its thorax and pygidium being 

 of equal or nearly equal length, and by its divided glabella. 



M. de VerneuiPs species, A. Barrandei, from the south of 

 France, is only known to me by name. Reasoning from ana- 

 logy, however, it may be fairly admitted that the two species 

 are distinct. 



Our new Canadian species somewhat approaches Barrande's 

 Asaphus nobilis, by the curious transverse furrow on its glabella. 

 In A. nobilis, however, the genal points of the head-shield ter- 

 minate in horns, and the segments of the thoracic and caudal 



