214 F, R. Cowper Reed— Fossils from Dufton Shales. 
species to some of the so-called varieties of Z. concentricus from 
Tyrone which Portlock described as distinct species. The form 
ascribed by B. Smith! to Portlock’s Z. elongatus,* under the designa- 
tion of 7. concentricus var. elongatus, has a nuchal spine similar to 
T. Nicholsont and more elongated cheeks and glabella than in the 
true 7’ concentricus; apparently there is a median tubercle present, 
and there is mention made of ‘‘ incipient furrows”’ at the base of the 
glabella which correspond to the pits in the axial furrows described 
in the Dufton species. But the pits in the fringe at the genal angles 
are more numerous in the Tyrone examples. In the form termed 
Tf. concentricus var. Portlockt by Smith,® it is remarked that the three 
rows of pits in front of the glabella tend to become confluent in 
a radial direction, as rarely in Z: Wicholsont. The Shropshire specimens 
referred to Z. concentricus have the pits of the concentric rows 
arranged alternately, so that the radial arrangement is lost (as in 
examples of this species from Cincinnati), whereas in many of the 
Welsh specimens there is a radial regularity observable. Barrande’s 
T. ornatus (Sternb.)* seems closely allied to our Dufton species in the 
shape of the head-shield, nuchal spine, pits in axial furrows, tubercle 
on glabella, and radial arrangement of the pits on the fringe; but these 
pits are more numerous and smaller. Further investigation will, it is 
believed, establish the specific independence of several British forms. 
EXPLANATION OF PLATE XVI. 
TrinucLeus NicHoLsonl, sp. nov. 
Fic. 1. Head-shield, with portion of thorax attached, showing impression of lower 
_ surface of fringe with concentric ridge and genal spines. x 2. 
», 2. Head-shield, showing ditto. x 2. 
», 3. Head-shield, showing upper surface of fringe, ete. x 23. 
,, 9a. Portion of fringe. x 10 
», 4. Head-shield. x 38. 
wy Oe Ditto. x 25. 
», 6. Impression of upper surface of fringe and cheek. x 2}. 
;, 7. Nearly complete head-shield. x 23. 
>, 7a. Side-view of same, showing nuchal spine. x 2. 
», 8. Head-shield, showing impression of lower surface of fringe. x 2%. 
,, 8a. Side-view of same, showing impression of concentric ridge. x 23. 
a EB Leeann, Se We 
Part II. 
(PLATE XVII.) 
ACIDASPIS SEMIEVoLUTA, sp. nov. Pl. XVII, Figs. 1-3. 
Head-shield semicircular, with middle part projecting behind base 
of cheeks. Glabella moderately convex, oval, widest across middle, 
well defined by strong continuous curved axial furrows; lateral lobes 
1 B. Smith, Proc. Roy. Irish Acad., 1907, vol. xxvi, sect. iB, No: 95h penl22. 
pl. viii, figs. 38, 4. 
® Portlock, Geol. Rep. Londond., p. 263, pl. iB, fig. 7. 
3 B. Smith, op. cit., p. 121, pl. viii, figs. 1, 2. 
_ 4 Barrande, Syst. Silur. Bohéme, vol. i, p. 623, pl. xxix, figs. 1-9; pl. xxx, 
figs. 41-60. 
