NOTE ON A NEW SPECIES OF TRIARTHRUS. 275 
NOTE ON A NEW SPECIES OF TRIARTHRUS FROM THE 
UTICA SLATE OF WHITBY, CANADA WEST. 
BY J. F. SMITH, JR. 
(Read before the Canadian Institute, 26th January, 1861.) 
The specimen here figured, was discovered about two years ago, in 
a piece of Utica Slate from Whitby. I 
had previously obtained, from the same 
locality, a side-piece of the head of a much 
larger individual, but did not describe it, 
as the specimen was too imperfect. The 
fact that this genus has been altogether 
described from fragments, may serve as an 
Triartivrus Canadensis. — anology for adding a new species under the 
same circumstances. The genus Triarthrus is said to differ from the 
genus Olenus, asregards the head-shield, by the facial suture of the latter 
genus terminating at the posterior margin of the buckler; while in 
the former, it terminates at the angles as in Oalymene. I do not 
think that this distinction will hold good as a generic character, for 
in the species here figured the suture does not terminate at the angles, 
but at the margin, as in Olenus. This distinction, however, is not 
well represented in the accompanying figure. I propose to call this 
new species Triarthrus Canadensis, as it is the third discovered in 
this Province. The only other species having long spines, is Triarthrus 
spinosus (Billings). By reference to Mr. Billings’ description (Can. 
Geol. Survey Rep., 1853-54, 55, 56, page 340) the difference in 7. 
Canadensis will become at once apparent. The horns of the former 
are slender and cylindrical, and point, with a slight curve, almost 
directly downwards to the eighth pair of pleure. In 7. Canadensis, 
they are flattish, and rather thick, with a groove running down the 
centre, and they extend at an angle of about 40°, evidently not farther 
than the fourth pair of pleuree. The specimen before mentioned, and 
the one here figured, are the only ones yet discovered. Good speci- 
mens are therefore likely to be rare. 
