DIONIDE LAPWORTHL 25 



Genus DIONIDE, Barrande. 

 1. Dionide lapworthi, Nicholson and Etheridge, 1880. Plate IV, figs. 1, 2. 



1880. Dionide lapworthi, Nicholson and Etheridge, Mon. Silur. Foss. Girvan, fasc. iii, p. 280, pi. xx, 



fig. 1. 

 1880. Dionide, sp., Nicholson and Etheridge, ibid., p. 294, pi. xx, fig. 3. 

 1899. Dionide lapworthi, Mem. G-eol. Surv., Silur. Eocks Brit., vol. i, Scotland, pp. 517, G72, 688. 



Specific Characters. — General shape elongated oval, gradually narrowing pos- 

 teriorly. 



Head-shield flattened, broadly semicircular, more than twice as broad as long, 

 wider than thorax ; curvature of anterior margin flattened ; posterior margin almost 

 straight. Glabella (imperfectly known) subquadrate, truncate behind, rounded 

 in front, nearly as broad as long, weakly convex, more than two thirds the length 

 of the head-shield and less than one third its width. Small median tubercle 

 present. A pair of short longitudinal or slightly oblique furrows indent its base, 

 starting from the occipital furrow and running forwards for about one third the 

 length of the glabella, but not reaching the axial furrows. Axial furrows distinct, 

 narrow, uniting in front of glabella. Occipital ring narrow (imperfectly known). 

 Cheeks broad, flattened, uniting in front of glabella ; surface covered with closely 

 set small pits with obscure radial arrangement near anterior lateral portions of 

 glabella, from which start several indistinct radiating fine lines running outwards 

 and backwards ; two of these lines are more conspicuous than the others, at first 

 diverging and then re-uniting near the genal angles. Narrow thickened smooth 

 border round head-shield, produced at genal angles into long straight slightly 

 divergent spines (? grooved) reaching back as far as or beyond posterior end of 

 body. Smooth straight neck segment behind cheeks, marked off by narrow furrow. 



Thorax of six segments, narrower than head, decreasing in width posteriorly. 

 Axis convex, as wide as pleurae, tapering gradually; each ring furnished with 

 transversely oval median lobe and triangular lateral lobes. Pleurae broad, flattened, 

 horizontal, straight, with abruptly truncate ends, and curved diagonal furrow; 

 surface covered with coarse pits. 



Pygidium very long, parabolic, of many segments. Axis tapering, wholly 

 segmented, showing 10 — 20 rings similar to those of thorax. Lateral lobes of 16 — 

 20 pleurae like those of thorax but narrower, obliquely bent back towards posterior 

 end of pygidium and decreasing in length. 



