Prof. E. J. Chapman on new Trilobites from Canadian Rocks. 1 1 



rowed to about half their length from the axis, and then crossed 

 obliquely by a curvilinear ridge. A second, but slighter, furrow- 

 runs along the lower edge ; and two short deep furrows, shaped 

 together like the letter V placed upon its side with the point 

 inwards, separate each pleura from its axis-segment. Beyond 

 the ridge the points are delicately striated. Fine punctures 

 occur upon the axis and also on the pleurae. On the latter the 

 punctures are larger and farther apart; and, when examined 

 through a magnifying glass, they appear to be of a semilunar 

 form, with the convex side turned inwards; they are likewise 

 more deeply indented at the convex side. 



Pygidium oval, with striated limb and well-developed taper- 

 ing axis. This terminates somewhat abruptly before reaching 

 the end of the pygidium. It contains from 12 to 14 segment- 

 markings, and a similar number are present on the side-lobes. 

 All are destitute of secondary furrows. Those on the side-lobes 

 bend downwards near their extremities, and merge into the 

 striated limb. The lower ones are nearly vertical. The whole 

 surface of the pygidium is covered with fine punctures, shaped 

 and arranged exactly like the punctures on the surface of the 

 thorax. Asaphus platycephalus, as mentioned by Professor Hall, 

 exhibits in some specimens a delicately punctured surface ; but 

 in the present species the punctures appear to be much more 

 striking. Our other new species, A. Halli, is also very visibly 

 punctured, although the punctures, as shown in our figures, are 

 too coarse and too far apart. 



The only specimens of Asaphus Canadensis hitherto obtained, 

 have been procured from the Utica schist (Lower Silurian) of 

 the townships of Whitby and Nottawasaga (localities about 80 

 miles apart), in Canada West. They occur in association with 

 Triarthrus Beckii. In length they appear to vary from about 

 an inch and a half ( = 38*1 millimetres) to about 5 inches 

 ( = 127 millimetres). I have not yet been able to observe the 

 under side, so as to make out the direction of the under sutures 

 and the form of the hypostoma. An isolated hypostoma, how- 

 ever, found near Whitby, probably belongs to this species. It 

 is badly preserved, but it appears to resemble very closely the 

 hypostoma of A. platycephalus. 



§ 3. Specific differences. — (1.) Asaphus Canadensis differs from 

 A, platycephalus, Stokes (Isotelus gigas, Dekay) ; A. eocpansus, 

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



the pleurae have almost invariably an upward curve, as in the figure of 

 A. Halli, on page 13. When the side-pieces or cheeks of the head-shield 

 are broken off, we may generally determine the nature of the genal angles 

 by this character. 



