ON SOME NEW TRILOBITES FROM CANADIAN ROCKS. 233 



breadth of each side-lobe, as 5 to 6. Pleurae, terminating in slight 

 points, and curving slightly downwards*; furrowed 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 punc- 

 tures are larger and farther apart ; and when examined through a 

 magnifying glass, they appear to be of a semi-lunar 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, tapering 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 extremi- 

 ties, and merge into the striated limb. The lower ones are nearly ver- 

 tical. The whole surface of the pygidium is covered with fine punc- 

 tures shaped and arranged exactly like the punctures on the surface of 

 the thorax. Asaphus platycephaliis, 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. Haiti, is also very visibly punctured ; although 

 the punctures, as shovra 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 eighty miles apart), in. 

 Canada West. They occur in association with Triarthrus Beekii. In 

 length they appear to vary from about an inch and a half (=38.1 milli- 

 metres), to about five 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, 

 however, found near Whitby, probably belongs to this species. It is 

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

 of A. platycephalus. 



* In the horned Asaphidse, and in nearly all the horned trilobites, the pleurse point down- 

 wards, whilst in the forms with rounded genal angles, the pleurae have almost invariably 

 an upward curve, as in the figure oi A. Halli, on page 236, 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. 



VOL. III. 



