BY JOHN MITCHELL. 44 5 



which is rounded; each posterior segmental ridge bears a row of 

 tubercles, as du also the axial rings; axial furrows distinct. 



Pygidinvi semi-ellipsoidal, moderately tumid and strongly 

 tubercuJate; proportion of length to width equals 3 : 4 approxi- 

 mately; axis has fourteen rings, prominent, dorsally depressed, 

 sides steep, contracting very gradually posteriorly to about half 

 the anterior width, terminating bluntly and somewhat overhang- 

 ing the border, the rings bearing tubercles which vary in number 

 with their spread from two or more on the posterior ring, to 

 eight on the anterior ones, and not exactly forming longitudinal 

 rows; axial furrows pronounced; pleurae very convex, arching 

 from the axial grooves at first gently and then steeply to the 

 narrow furrow separating them from the border, where all the 

 segments, except the anterior pair, end, segments ten in number, 

 each succeeding one having a gently backward trend, and dimin- 

 ishing in length till the last two pairs are represented by mere 

 tubercles. Each segment bears a row of tubercles along the 

 posterior ridge varying in number with its length, from one to 

 ten, and perhaps in some instances more; medial segmental 

 furrows wide and shallow, reaching to the faint furrow within 

 the border; the border itself is fairly wide, and thickened, and- 

 in normal specimens, has the same convexity as the pleura] ribs; 

 it bears a row of conspicuous tubercles usually placed in line 

 with each rib, and three to five behind the axis, these tubercles 

 being occasionally elongated or double; when the thickened por- 

 tion is removed, the undersurface shows concentric striations, 

 which is a common feature in the Proetidte. Only the first pair 

 of the pleural segments interrupts the continuity of the l)order. 



Ohs —This species is (juite singular. Its outstanding features 

 are:— 1. The narrow, straight-sided glabella. 2. 'J'he crowded 

 and conspicuous tuberculation uf the glabella. 3. The equality 

 of the lengths of thepygidium and thorax. 4. The width of the 

 thorax, which equals half the total length of the complete indi- 

 vidual. 5. The closeness of the eyes to the axial groove. G. The 

 straightness of the anterior branches of the facial sutures, and 

 their parallelism to the axial furrows. 



Dimensions: total length of an individual not quite mature. 



