10 EXPLANATION OF THE PLATES, 
Fic. 5.—OLENUsS CATARACTES, Salter. 
Decade 11, pl. viii., fig. 14; Mem. Geol. Surv. vol. iii., p. 300. pl. v., fig. 23. 
From the original figure in Decade 11, pl. viii., fig. 14. In the description 
of this species in the Decade cited, Mr. Salter observes that the number 
of body rings should be 15, distinguishing it in that respect from the pre- 
ceding species, O. micrurus, which has 14 : as the figure from the Decade is 
here copied, the error, if such it be, is also repeated. 
Lower Lineura FrLacs.—Maentwrog Waterfall, Merionethshire ; in black 
shales full of Agnostus princeps; Treflys, east of Criccieth, Caermarthen- 
shire, North Wales. 
Fig. 6.—a, b. OLenus HUMILIS, Phillips. 
Memoirs Geological Survey, vol. ii., part I., p. 55, figs. 4, 5, 6. Memoirs 
Geological Survey, Decade 11, pl. viil., figs. 9-11. 
a. From Memoirs Geological Survey, vol. iii. pl. v., fig. 12; this figure being 
apparently reduced from that in the Decade above cited, fig. 9. The natural 
size of this very minute Trilobite is shown by the line drawn near it. 
b is reduced in the same proportion from the head figured in the same Decade, 
pl. viii., fig. 10. The author well remembers the difficulty experienced in 
making out the drawings of these very minute Trilobites for Professor J. 
Phillips’ Memoir, now nearly twenty years ago; since then much better 
specimens have been procured, some showing the entire animal, as in the 
figure we have copied at 6 a. 
Urrer Linauta Frags.—Only known in the black shales of Malvern at 
Fowlet’s Farm, and White-leaved Oak Farm, &c., where it occurs in con- 
siderable abundance with other species of the same genus. 
Fig. 7.—DIKELOCEPHALUS (?) CExtiIcus, Salter. 
Mem. Geol. Surv. vol. iii., p. 304, pl. v., fig. 21, 22. 
From figure 22 in the work above cited, representing the tail or pygidium. 
only. 
Urprer Lineuta Fracs.—Ogof-ddu, east of Criccieth, North Wales, in 
black slate. 
Fig. 8.—CoNocorRyPHE InviTA, Salter. 
Geological Survey, Decade 11, pl. vii., fig. 6. Conocephalus invitus, Siluria, 
third edition, p. 47, Foss. 7, fig. 1. Memoirs Geological Survey, vol. 
iii., pl. iv., figs, 5, 6, 7, pl. vil. fig. 6. 
From the original figure, Decade 11, pl. vii., fig. 6, portions of the head and 
tail only of this species have been cdllected, the figure is completed in out- 
line. 
Urrrr Linevra Fracs.—Penmorfa Church, and Carreg-wen, Tremadoc ; 
Ogof-ddu, near Criccieth, North Wales. 
