54 The Ottawa Naturalist. [Aug. -Sept- 



from the back, is represented on either side by a dimple situated 

 midway between the side and the centre of the glabella, and 

 midway between the furrows anterior and posterior to it. The 

 glabellar furrow nearest the front is a short diagonal groove 

 starting just back of the point of union between the anterior 

 end of the eye lobe and the glabella, and occupying the central 

 portion of the distance from the side to the centre of the glabella. 

 Surface of the cephalon an irregular network of raised inoscu- 

 lating lines more or less radial to the outer margin. Pleurae 

 of two distinct types, an anterior normal set of fourteen and a 

 posterior rudimentary set of 29 (or more, the end is broken 

 away) separated by a spine-bearing segment. Ihe ends of the 

 first fourteen ribs become progressively longer toward the 

 posterior end of the trilobite, and the fourteenth pair almost 

 surround the rudimentary 29. These are further protected by 

 the spine on the fifteenth segment, which is likewise extended. 

 The rudimentary ribs differ little in width of axis from those 

 which precede them, but the sides are very small. Pleural 

 grooves broad, flat, and almost parallel-sided in those forming 

 the middle portion of the trilobite. Toward the spine-bearing 

 fifteenth segment the pleurae become relatively much wider for 

 their length, and the pleural groove cuts more and more dia- 

 gonally until in the thirteenth and fourteenth it cuts directly 

 across from the anterior inner corner to the posterior outer 

 corner. Rudimentary segments almost plain, pleural grooves 

 being indistinct or wanting. The taper to the 29 rudimentary 

 segments which have been preserved is so gradual as to render 

 it extremely probable that there were many more than 29 

 segments anterior to the pygidium. 



The fourth, fifth, and sixth pleurae on the right side of the 

 specimen described have suffered injury, being broken off 

 close to the axis at such a time or in such a manner that the 

 ends have healed, and show a tendency toward a normal ter- 

 mination. The fifth one in particular is broken clear across, 

 and in it the pleural groove stops just inside of the newly curved 

 margin; the fourth and sixth were broken across transversely 

 so as to leave the greater portion respectively of the upper and 

 lower margins. This particular trilobite is as large or larger 

 than the largest that has so far been discovered in the Lower 

 Cambrian of British Columbia or Alberta. If we assume that 

 the accident occurred during the youth of the trilobite, we 

 must grant that these early forms did not have the power of 

 renewing broken or lost portions, but this conclusion is negatived 

 by its ability to heal up the broken ends and fashion them off. 

 The accident was, therefore, probably of recent occurrence. 

 And since it must have happened during his maturity, we are 



