F. R. Cowper Reed—Fossils from Dufton Shales. 213 
with the second or third thoracic segment, and the posterior and lateral 
edges of the head-shield meet here at about 75°-80°. Neck-segment 
behind cheeks narrow, rounded, marked off by distinct but weak 
furrow. Surface of fringe coarsely granulated. 
Thoracic axis about one-sixth the width of thorax, narrow, prominent, 
cylindrical, with pair of deep pits in furrows between the rings inside 
and above axial furrows. Pleurse of usual type, narrow, horizontally 
extended, flat, with strong diagonal furrow running to obliquely 
truncate tip. Inner edge of backwardly produced genal angles of 
fringe overlaps ends of first three pleure. 
Pygidium broadly triangular; axis long, narrow, conical, reaching 
posterior edge, less than one-fifth width of pygidium, composed of 
9-10 rings, of which the first 3-5 are distinct and well separated by 
transverse furrows deepest at sides. Lateral lobes flat, horizontal, 
with traces of 4-6 radiating fine grooves on each side separating the 
flat pleuree and corresponding to axial rings. Margin of pygidium 
bevelled, steeply inclined. 
mm. 
Dimensions. Length of head-shield (without spine) . . - 10-15 
Width of head-shield . 0 , : . 20-25 
Remarks.—The characters and shape of the glabella separate this 
species from 7’ seticornis, for it is not divided into a swollen frontal 
lobe and depressed cylindrical neck, though the more or less inclined 
fringe and position of the concentric ridge on its lower surface and 
median tubercle on the glabella are featuresin common. 7. Bucklandi, 
Barr., as represented in the Girvan district,) has the glabella 
differmg in the same way, and the genal angles are much more 
produced backwards. The shape of the glabella and presence of 
nuchal spine are much hke Z. Bureaui, Oehlert,*? but otherwise the 
head-shield is distinct. In 7. concentricus, Eaton,* it is the glabella, 
not the occipital ring, which is produced backwards into a spine; 
only the outermost row of pits on the fringe is separated off by the 
concentric ridge on the lower surface, and there are no lateral slits 
or pits near the base of the glabella; the radial arrangement of the 
pits on the fringe is not as a rule so well marked in any of the 
American specimens which I have examined, and there is no median 
tubercle on the glabella, though its general shape is very similar. 
The British forms referred by various authors to 7. concentricus vary 
so greatly that probably more than one species, or at any rate several 
distinct varieties, have been included. Amongst the varieties recognized 
by Salter, Z. favus’ bears some resemblance to 7. Micholsoni in the 
shape of the glabella with pits at its base and in the presence of 
a nuchal spine, but the fringe has different characters. 7. fimbriatus, 
Murch.,° does not seem to be closely allied. 
We may draw particular attention to the resemblance of this 
1 Reed, Girvan Trilobites (Paleont. Soc.), 1903, pt. i, p. 10, pl. i, figs. 10-14. 
* Oehlert, Bull. Soc. Géol. France, 1895, vol. xxiii, p. 300, pl. i. 
a 3 er Paleont. N.Y., 1847, vol. i, pp. 249, 255, pl. lxv, figs. 4a-c; pl. Ixvii, 
gs. la-h. 
4 Salter, Mem. Geol. Surv., vol. ii, pt. i, pl. ix, fig. 5; id., Dec. Geol. Surv., 
1853, vol. vul, pl. vii, p. 6. 
° McCoy, Brit. Paleoz. Foss., 1851, p. 146, pl. iE, fig. 16. 
