DIONIDE RICHARDSON! 27 



long curved spines, backwardly directed, longitudinally striated, and longer than 

 whole body. Glabella convex, subquadrate, slightly contracted across middle,' as 

 broad as long-, and extending fully three fourths the length of the head-shield, 

 truncated posteriorly. Two furrows, deep at first but rapidly growing faint, 

 start from occipital furrow at base of glabella, run forwards rather obliquely, 

 and die out before reaching axial furrow about halfway up sides of glabella, thus 

 imperfectly defining a pair of triangular basal lobes. Glabella bears a strong 

 median tubercle (? base of spine) at about one third of its length from occipital 

 furrow. Surface of glabella finely punctate. Occipital furrow well marked. 

 Occipital segment of moderate width. Cheeks broad, uniting in front of glabella ; 

 gently convex in centre but sloping down to sides and front. Surface of cheeks 

 irregularly pitted. Traces of two raised nervures from sides of glabella towards 

 genal angles. Narrow smooth border round head-shield, with a regular single row 

 of rather larger pits just inside it. Genal spines long, curved, striated. Occipital 

 furrow strong, curved forwards, marking off smooth segment behind cheeks. 



Thorax of six segments. Axis feebly convex, about two thirds the width of 

 pleural portion, gently tapering posteriorly. Axial rings furnished with sub- 

 triangular lateral nodules and narrow median ridge, forming continuous raised 

 band down middle of axis. Axial furrows strong. Pleura? horizontally extended, 

 straight, with truncated ends slightly bent back, and strong oblique pleural furrow. 

 Anterior part of each pleura marked by transverse parallel closely placed ruga?; 

 posterior part smooth and more or less swollen near axial furrow. 



Pygidium parabolic, as long as wide ; axis conical tapering, not quite reaching 

 posterior margin ; of 16 — 18 rings, of which the anterior ones possess the characters 

 of those of the thorax. Lateral lobes flattened, horizontal; consisting of 12 — 15 

 furrowed pleura? ornamented as in thorax, but dying out near margin. 



Hypostome with broadly oval convex bod}', tuberculated ; very narrow posterior 

 border and expanded rounded flattened anterior wings, well marked off from body. 



Remarks. — Several nearly perfect individuals as well as detached portions are 

 now available to define this species, which varies somewhat in appearance according 

 to its state of preservation. The glabella in the specimens figured on PL I Y, tigs. 

 4 and 5, are unduly wide and subcircular in appearance owing to crushing. 



Affinities. — This species is very closely allied to Dionide formosa, Barrande, 2 

 but seems to differ in the course of the glabellar furrows, the characters of the 

 thoracic and pygidial axis, the ornamentation of the pleura 1 and of the genal 

 spines, and the fewer segments in the pygidium. The difference in the pleural 

 ornamentation is very marked, and Nicholson and Etheridge (M., p. 293) suspected 

 that this form would have to be separated from D. formosa. The name richardsoni 



1 The strong constriction shown in PI. IV, tig. 3,islargely due to the imperfed preservation of the 

 glabella in this specimen. 



- Bamuide, 'Syst. Silur. Boheme,' vol. i, p. Gil, pi. xlii. figs. 24 28 : Suppl. i. p. 50, pi. i, Bg. 18. 



