258 



MINERALS AND GEOLOGY 



FIG. 174. 



P. Bufo, is represented in Figure 1 74. The genus Dalmanites is closely 

 allied to Phacops, possessing like the latter an anteriorly expanded gla- 

 bella, with coarsely-reticulated eyes, and facial suture 

 terminating at the sides of the head-shield. But it 

 is distinguished by distinctly marked lateral fur- 

 rows on the glabella and by its pointed pleurae. 

 The head-shield is also horned at its genal angles, 

 and the pygidium in some species ends in a long 

 spine. This is the case with our I), limulurus, 

 Figure 175, from the Niagara (Upper Silurian) 

 formation, but the caudal spine is only seen in 

 well preserved examples. The genus is exclu- 

 sively Silurian. 



In the group of Conifrontes, the distinguishing 

 character is the conical form and comparatively 

 small size of the glabella, but in other respects 



b Phacops bufo : Green. 



these trilobites closely approach the Frontones Comiferous and Ha- 



mllton Formation 



the head-shield as a rule exceeding the pygidium 

 in size, and the body-axis being continued into the latter, so as to ren- 

 der the line of separation between the thorax and pygidium scarcely 

 distinguishable. Some ot the more typical genera comprise : Olenus, 

 Harpes, Conocephalites, Triarthrus, Calymene and Homalonotus. 

 The genus Olenus, with from twelve to sixteen 

 narrow, pointed body-rings, and very short pygi- 

 dium, is of doubtful occurrence in Central Cana- 

 dian strata, unless the " Loganellus," discovered 

 by Mr. T. Devine in the Levis formation of Quebec, 

 belongs to it. The type is essentially Cambrian. 

 The genus Harpes is both Silurian and Devonian. 

 It has a very large horse-shoe-shaped head-shield, 

 with broad, perforated border, but the glabella is 

 short and conical. The body-segments vary from 

 twelve to twenty-five or twenty-six in number, 



Figure 176 



shews the head-shield (with eyes connected by a 

 raised band, as in Olenus) and part of the many-ringed thorax of 



FIG. 175. 



Dalmanites Umalurus : and the pygidium is very small. 



Harpes Ottwaensis (Billings) from a specimen obtained from the 

 Trenton Formation by Dr. Grant of Ottawa. The genus Conocep) 



