ON SOME NEW TRILOBITES FROM CANADIAN ROCKS. 235 



Finally, apart from the absence of secondary furrows on the pygi- 

 dium segments, Asaphus Canadensis differs from the generally 

 admitted species of Ogygia, by the following characters : 



(1.) From O. Buchii, Brongniart ; and 0. (?) 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. (?) Besmaresti, 

 Brong. ; O. (?) Brongniarti, Roualt ; and O. (?) Bdivardsi, Roualt — 

 by the angular junction of the branches of its facial suture above the 

 glabella. 



(3.) From O. radians, McCoy — by the large number of the seg- 

 ment-markings on the axis of its pygidium, 0. radians exhibiting only 

 three. The head-shield of 0. radians is unknown, but McCoy 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 OF ASAPHUS FROM CANADIAN ROCKS. 



The accompanying figure represents a new species of Asaphus, from 

 the Trenton limestone (Lower Silurian), of Peterborough, 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 to 2, or thereabouts ; relative lengths of head-shield, thorax, 

 and pygidium, as 1 : 0.87 : 0.87. 



Head-shield obtusely pointed anteriorly, and much resembling that of 

 A. platycephalus in its general outline. Limb striated with concentric 

 lines ; genal angles rounded ; facial suture as shewn in the figure. 

 The branches unite above the glabella in a well-defined angle, almost 

 touching the extreme anterior margin 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 

 pecuUarity not exhibited bv the facial sutures of A. platycephalus (?) 

 or A. Canadensis. Glabella, feebly raised, and divided into two dis- 

 inct portions ; 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 shewn in the figure), strongly marked in 



