ACIDASriS TERRIBILIS. 37 



overhanging lateral lobes ; two pairs of lateral lobes present, Ijotli completely 

 marked off from median lobe by continuous furrow; anterior pair rounded, 

 subquadrate, about one-third the length of the glabella and less than one-third 

 its width, incompletely marked off from posterior pair by short horizontal furrows, 

 deep at inner end and starting from median longitudinal furrows, but dying out 

 before reaching axial furrows ; posterior pair of lateral lobes sub-oblong, longer 

 than wide, nearly half the length of the glabella and nearly one-third its width. 

 Axial furrows narrow, weak, not deeply impressed, convergent anteriorly, nearly 

 straight for greater part of length, but arched in strongly at base. 



Meso-occipital ring broad, marked off from base of median lobe by strong- 

 furrow, furnished with a median pair of stout divergent spines rising up vertically 

 from surface. 



Fixed cheeks large, convex, swollen, subtriangular, arched down, with a width 

 at their base equal to two-thirds that of the glabella. Eyes apparently absent, or 

 very small, situated far forward, opposite first lateral furrows of glabella. Ocular 

 ridges very weak, short, indistinct. Pleuro-occipital segment narrow at inner 

 angle of fixed cheeks, but widening to their rounded outer angle. Free cheeks 

 small, narrow, crescentic, about half the width of the fixed cheeks, with outer 

 edge strongly arched outwards and forwards ; genal angles rounded, with 

 prominent tubercle or short spine just inside margin ; lateral border flattened, 

 broad, smooth, marked off by strong marginal furrow, and armed with 14 — ]G (?) 

 small marginal spines directed forwards and outwards and decreasing in length 

 from back to front. Facial sutures obscure. Surface of head-shield ornamented 

 with coarse tubercles of two to three sizes, irregularly scattered. 



Thorax composed of nine segments. Axis strongly convex, cylindrical, about 

 one-fourth the width of the thorax; axial rings broad, with Avell-marked nodular 

 lateral swellings and with median pair of short divergent spines standing up 

 vertically and directed obliquely outwards like those on occipital ring ; general 

 surface of rings tuberculated. Pleurte broad, horizontally extended for inner two- 

 thirds of length, outer third strongly bent down ; furnished with narrow anterior 

 marginal ridge produced into short, slightly recurved spine armed with minute 

 denticles ; rest of surface of inner part of pleurae composed of a rounded, elevated, 

 broad semi-cylindrical ridge, which at the point of bending is produced into a long- 

 free cylindrical curved spine projecting outwards and upwards in a different plane 

 to the anterior pleural spines. General surface of pleurae ornamented with small 

 tubercles, especially numerous on anterior ridge. Last pair of larger pleural 

 spines bent sharply backwards and parallel. 



Pygidium transverse, about three times as wide as long, with horizontal 

 flattened pleural lobes ; anterior margin straight, with thickened rim bearing a 

 tubercle near each end ; posterior margin with indistinct border and armed with 

 series of spines ; first pair of spines small, straight, directed backwards, starting 



