RAYMOND: SOME M.w ORDOVICIAN TRILOBITES. 279 



Anisonoti s, gen. now. 

 Anisonoi i a quu i llis (Billings). 



Shwnardia glacialia Billings, Palaeozoic foss. Canada, 1865, 1, p. 238, fig. '270. 



Entire trilobite oval in outline, nearly as wide as long, the greatest width 

 being at the back of the cephalon. The cephalon is strongly convex; the 

 thorax and pygidium nearly Hat except for the axial lobe, which is narrow and 

 elevated. 



The cephalon is trinuclear, the swollen glabella rising above the mound-like 

 fixed cheeks. The glabella extends two thirds of the length of the cephalon 

 (measured on the curvature) and shows at the sides four pairs of pits. The 

 last pair represent the neck-furrow, and the others ( he fourt h, third, and second 

 pairs of glabellar furrows. The first and fourth pairs of pits are much less con- 

 spicuous than the others. The elevated glabella is bounded by a pair of 

 narrow furrows which converge backward and outside t hese is a pair <>f furrows 



which are parallel to the axis of the head. Between the parallel and the con- 

 verging furrows are a pair of only slightly elevated triangular ridges, the apices 

 pointed forward. 



Outside the parallel furrows on the cephalon there are two evenly rounded 

 mounds, limited on the inside and hack by Straight furrows intersecting at 

 right angles and at the front by a curving depression which joins the dorsal 

 furrows opposite the anterior glabellar furrows. In this depression there is 

 on each side a narrow hut distinct eye-line which curves backward around 

 the mound and continues to the border of the cheek, meeting it at the horizon 

 of the neck-furrow. In front of this furrow and in front of the glabella t hen- 

 is a rather abrupt bulging slope to the margin, which appears to he somewhat 

 thickened, but probably without rim or brim. The type being exfoliated, 

 gives the appearance of a very narrow r brim on the front. 



At the genal angles the fixed cheeks are drawn back into short la pets which 

 extend behind the neck-ring. These lapets are semicircular in outline, and 

 it is difficult to decide whether they are the actual genal angles, or whether 

 they were enveloped by spines belonging to the free cheeks. In front of the 

 angles there is a slight sinuosity in the side of the cheek, and along this part 

 the border which is present on the front of the cephalon is absent. This 

 seems to indicate that free cheeks should be present, but very narrow ones 

 :i- in most species of Ampyx. These cheeks would probably have borne the 

 genal spines. 



The anterior portion of the cephalon is covered with very fine wavy lin"- 

 parallel to the anterior edge. 



The thorax has seven segments, and does not taper from front to back. 

 The axial lobe is narrow, one fifth of the total width, and strongly elevated. 



The pleural lobes are flat, each pleuron bearing a linear groove whose course 

 is at right angles to the axis. The first two segments do not extend quite so 



