ORDOVICIAN TRILOBITES FROM THE TOURMAKEADY LIMESTONE 
TYPE SPECIES. Celmus granulatus Angelin, 1854, Skarpasen, 
Ostergétland, Sweden; by monotypy. 
OTHER SPECIES. Glaphurina? insolita Tjernvik, 1956; Celmus? 
longifrons Poulsen, 1965; Ischyrophyma tuberculata Whittington, 
1963; Ischyrophyma tumida Whittington, 1965; Ischyrophyma? sp. 
indet. of Whittington (1963); the specimen figured by Whittington 
(1965: pl. 19, figs 16, 19, 20) as Ischyrophyma? sp. indet. is a 
calymenid related to or conspecific with his ‘aff. Calymenidius sp. 
ind.’ (Whittington 1965: pl. 59, figs 10, 12-15); work in progress on 
silicified Newfoundland faunas indicate this taxon is a species of 
Sthenarocalymene Siveter, 1977. 
Celmus michaelmus sp. nov. 
Pl. 14, figs 1-17; Pl. 15, figs 1, 2, 5-9; Pl. 16, figs 11, 20 
1975 Celmus sp. Fortey & Owens Fig. 1A,B 
ETYMOLOGY. Latin, a mouse called Michael (see Pl. 15, fig. 6a). 
DIAGNOsIS. Dorsal sculpture densely tuberculate; several exsagittal 
rows of tubercles on anterior fixigena; posterolateral part of librigenal 
lateral border with sparse or absent tubercles, but prominent raised 
lines subparallel with margin; pygidium with nearly elliptical out- 
line in plan view; pygidial flanges circular and prominent. 
HOLOTYPE. Pygidium, It. 26123 (Pl. 14, fig. 4); paratypes It. 
12853, 12854, 26120-26122, 26124-26141, 26168, 26169. 
DESCRIPTION. Some of the silicified material upon which this 
species is based has suffered distortion; for example, the original of 
Pl. 14, fig. 6 has been foreshortened, and that of Pl. 14, fig. 3, 
elongated sagittally. The holotype, and such specimens as that 
figured on PI. 14, fig. 2, are considered close to the undistorted state, 
and it is upon these that descriptions of proportions are based. 
Cranidium as wide (tr.) at the posterior margin as long (sag.), this 
being three-quarters the width across the palpebral lobes; glabella 
about 1.5 times longer than wide, the maximum width being at L1 
where the glabella bulges outwards before tapering gently anteriorly; 
S1 deep and distinct, the outer part slightly wider and almost 
transverse, the inner part geniculated backwards and on most speci- 
mens just falling short of reaching the occipital furrow (PI. 14, fig. 7, 
in which it does, is also distorted); S2 is short, transverse, close to the 
anterior end of the palpebral lobe; glabella encroaches on the border, 
but at least some part of the border is visible in dorsal view; fixigenal 
and eye position are as in all other species of the genus; the palpebral 
lobes carry three or four prominent tubercles. 
Librigena retains a knob at the genal angle, which is a remnant 
genal spine; on a small example (Pl. 14, fig. 12) it is much more 
prominent; bevelled border bears three or four very prominent raised 
lines which extend as far as the knob; a few scattered tubercles may be 
present between the lines; the elevated eye has a smooth eye socle 
beneath it, at its anterior end, a small, inflated lobe (see PI. 15, fig. 1); 
doublure extends beneath border (Pl. 14, fig. 17), and carries an 
exterior groove on its posterolateral edge, which may have accommo- 
dated pleural tips upon enrollment (see Bruton 1983, pl. 28, fig. 2). 
Thoracic segment shows general convexity of body (PI. 15, fig. 
2b); anterior ridge terminates in an articulatory notch; posterior band 
continues distally as a spine. 
Minute pygidium is known from good isolated material; it com- 
prises a single segment, with an articulating half-ring; posterior 
margin densely covered with raised lines subparallel to margin, and 
narrow doublure (PI. 15, fig. 6c) with fine terrace lines; pygidium 
bears a pair of flat, rounded flanges which project backwards; the 
surface of the flanges is smooth. 
105 
The rest of the axial part of the exoskeleton, and the genal fields, 
is densely tuberculate; in some specimens the librigenal tubercles 
are of two sizes (PI. 15, fig. 1), but this is less clearly so in others (PI. 
14, fig. 11). 
DISCUSSION. This species is very similar indeed to the type spe- 
cies, Celmus granulatus (see Jaanusson 1956, Bruton 1983) from 
the Kundan stage of Sweden. Cephalic differences are trivial. The 
distinctive lobe at the anterior end of the eye socle of C. michaelmus 
is not mentioned in a detailed description by Bruton (1983, p. 216), 
but is visible on his figures (ibid, pl. 28, fig. 14). The sculpture on the 
Irish species is denser; for example the anterior fixed cheek of C. 
granulatus shows a single row of tubercles except at the anteriormost 
end, while several rows are present along its whole length in the new 
species (Pl. 14, figs 1c, 2c, 6b). The raised lines which extend to the 
genal spine remnant on the librigenal border of C. michaelmus stop 
well short of it in C. granulatus, and the portion of the border in front 
of the genal angle is far more densely tuberculate in the latter 
species. Finally, the prominent pygidial flanges of the Tourmakeady 
species are much better developed than a homologous pair of low 
ridges in C. granulatus (Bruton 1983: pl. 28, figs 10, 12), and the 
pygidium of the Irish species has an elliptical, versus trapezoidal, 
outline in plan view. 
Genus DIMEROPYGE Opik, 1937 
TYPE SPECIES. Sphaerexochus minutus Nieszkowski, 1857, Mid- 
dle Ordovician, Kukruse beds, Estonia; by monotypy. 
Dimeropyge? ericina sp. nov. 
Pl. 15, figs 15-17; Pl. 16, figs 17-19, 21-23 
ETYMOLOGY. Latin, of a hedgehog. 
DIAGNOSIS. Elongate glabellar spines retained in holaspid; two 
pairs of glabellar spines, four pairs of fixigenal spines; librigena 
carries two spines on genal field and a few on border. 
HOLOTYPE. Cranidium, It. 26150 (Pl. 15, fig. 15); paratypes It. 
26151, 26152, 26170-26175. 
DESCRIPTION. We have not discovered a pygidium of this unusual 
species, but the cephalic parts are so distinctive that it can be named 
as new. 
Glabellar outline is best seen on the inner surface of the cranidium 
(Pl. 15, fig. 15b), which shows it extending to two-thirds cephalic 
length, convex (tr.), defined by deep axial furrows; width at LO wider 
(tr.) than in front, thereafter expanding gently in width anteriorly to 
rounded front; LO carries a pair of long, stout spines; two equally 
stout pairs are present on the glabella; fixigena are wider than 
glabella at posterior margin; they, too, carry spines, which can be 
matched with the glabellar ones, since one pair on the rather poorly 
defined posterior border matches the occipital segment, and there 
are two pairs anterior to this matching those on the glabella. In 
addition, there are prominent spines on the posterolateral cranidial 
corners; the anterior border, however (Pl. 15, fig. 16b) is without 
spines; the palpebral lobe is inconspicuous at cephalic mid-length. 
Librigena has a prominent, and somewhat elevated eye lobe; on 
the genal field there are two spines; the lateral border is well defined, 
rounded, and carries only two or three comparatively subdued spines 
at its mid part; a thoracic segment can be confidently associated 
because it shows paired axial spines, and also two pleural spines, the 
inner one at the point of downward geniculation of the segment; the 
tips of the spines appear to be perforated. 
