New Species of Trilobiles. 381 



seven of the pleurae and the impressions of eight of the segments 

 of the axis, and according to such evidence as can be gleaned 

 from the measurement of these, the thorax nust be thirteen lines 

 in length and the axis eleven lines wide at the last segment. 



One of the specimens is a pygidium 3|jnches wide, and must 

 have belonged to an individual over eight inches in length. 



This species closely resembles I. Davisii, Salter (British Fos- 

 sils, Decade 2, PL 2.) but in that species the anterior margin of 

 the pygidum is straighter, the lateral angles not so decidedly trun- 

 cated, the pleurae more abruptly bent, and the fold under the pos- 

 terior margin broader. From these differences in the pygidium, 

 it may be inferred that the head when discovered will exhibit 

 other grounds for specific distinction. 



Locality and formation. — Anticosti, Hudson River Group, and 

 Middle Silurian. 



Amphion Canadensis, (n.s.) 



a b 



Fig. 12. 

 a Glabella. b Pygidium. 



Desertion. — The glabella in the only fragment of the head 

 that I have seen is sub-quadrate, a little more than two lints in 

 length and the same in width, a little narrower behind than in 

 front, the sides straight or gently concave, the front margin con- 

 vex, and the posterior margin concave. It is divided into four 

 lobes by three pairs of farrows. The posterior furrow extends 

 entirely across and is arched forward in the middle to correspond 

 with the concavity of the posterior margin. The other four fur- 

 rows extend rather more than one-third across. The two poste- 

 rior lobes occupy a little less than half the whole length. The 

 front margin of the anterior lobe has a short furrow in the mid- 

 dle and an oblique one on each side half-way between the middle 

 and the anterior angles. The glabella is moderately convex, and 

 the sides are separated from the cheeks by deep narrow furrows. 



Pygidium with six segments in the conical axis and ten ribs in 

 the side lobes, five on each side. The anterior pairs of ribs at 

 first project outwards for about one-third their length or a little 

 less, when they make a short curve and become nearly parallel 



