14 Prof. E. J. Chapman on new Triluhites from Canadian Rocks. 



Finally, apart from the absence of secondary furrows on the 

 pygidium-segments, Asaphus Canadensis differs from the gene- 

 rally admitted species of Oyygia by the following characters : — 



(1.) From O. Buchii, Brongniart, and O. (?) Portlockii, Salter, 

 by the branches of the facial suture being united on the upper 

 part of the head-shield. 



(2.) From O. (?) Guettardi, Brongniart; O. (?) Desmaresti, 

 Brong. ; O. (?) Brongniarti, Rouault ; and 0. (?) Edivardsi, 

 Rouault — by the angular junction of the branches of its facial 

 suture above the glabella. 



(3.) From O. radians, M'Coy, by the large number of the 

 segment-markings on the axis of its pygidium, O. radians ex- 

 hibiting only three. The head-shield of O. radians is unknown ; 

 but M'Coy refers the species to Ogygia, on account of the short 

 segmental furrows between the larger markings on the side- 

 lobes of the pygidium. 



II. On a second new species o/" Asaphus /rom Canadian Rocks. 



Fig. 2 represents a new species of Asaphus, from the Trenton 

 limestone (Lower Silurian) of I'ctcrborough and other localities 

 in Upper Canada. The same form is believed to occur also in 

 the Utica schist. 



General outline a broad oval ; length to breadth as 3 : 2, or 

 thereabouts ; relative lengths of head-shield, thorax, and pygi- 

 dium, as 1 : 0-87 : 0-87. 



Head-shield obtusely pointed anteriorly, and much resembling 

 that of A. idatycephalus in its general outline. Limb striated 

 with concentric lines ; gcnal angles rounded ; facial suture as 

 shown in the figure. The branches unite above the glabella in 

 a well-defined angle, almost touching the extreme anterior mar- 

 gin of the head-shield ; and they terminate at the lower margin, 

 about midway between the glabella and the genal angles. Where 

 they join this lower margin, they make a short curve inwards 

 (see the figure), somewhat as in A. expansus, — a peculiarity not 

 exhibited by the facial sutures vti A. plati/ce])halus (?) or A. Cana- 

 densis. Glabella I'eebly raised, and divided into two distinct 

 ])ortions ; the lower portion, of a semi-oval shape, is defined, as 

 it were, by a prolongation of the body-axis. Directly above this 

 an undulating furrow occurs (as shown in the figure), strongly 

 marked in 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 a])pear to be of 

 the usual Asaphus type; they are somewhat wide aj)art; the 

 breadth between their central points, to the entire breadth of 

 the head-shield across them, is as 5 : 9. Except at the striated 

 limb, the whole surface of the head-shield is finely punctured. 



