ORDOVICIAN TRILOBITES FROM THE TOURMAKEADY LIMESTONE 
Symphysurus arcticus Fortey, 1975a: pl. 21). On present evidence, 
the only feature that might indicate that the Irish material is distinct 
is a librigenal field that is smaller in area, particularly posteriorly, 
with the posterior section of the facial suture concomitantly shorter 
(Pl. 1, fig. 2a). 
Family RAPHIOPHORIDAE Angelin, 1854 
Genus AMPYX Dalman, 1827 
Ampyx cf. toxotis Fortey, 1975a Pl. 1, figs 11, 12 
MATERIAL. Assigned specimens It. 25949, 25950. 
DISCUSSION. The Irish species, represented by only two speci- 
mens, shows strong similarity to Ampyx toxotis in its unusually long 
cranidial posterior border, relatively small and sub-rounded gla- 
bella, effaced pygidial axis, and relatively deep furrow along the 
pygidial anterior margin. The species differ in that the cranidial 
posterior border of the Irish species is not as exsagittally elongate, 
and the border furrow is better impressed, particularly proximally. 
Family STYGINIDAE Vogdes, 1890 
Genus PROTOSTYGINA Prantl & Pribyl, 1949 
TYPE SPECIES. Jllaenus bohemicus Barrande, 1872, Sarka Forma- 
tion (Llanvirn), Czech Republic; by monotypy. 
Protostygina coronula sp. nov. 
Pl. 2, figs 1-6, 8 
ETYMOLOGY. Latin, small crown. 
DIAGNOsIS. Anterior border furrow long and relatively deep; axial 
furrows strongly impressed posteriorly; SO well impressed; pygidial 
axis elevated sharply from pleurae; pygidium with sagittal length 
about 60% of maximum width. 
HOLOTYPE. Cranidium, It. 25952 (Pl. 2, fig. 1); paratypes It. 
25953-25958. 
DESCRIPTION. This is based primarily on the largest adult speci- 
mens. 
Cranidium with sagittal length subequal to, to very slightly longer 
than, the width (tr.) across midlength of palpebral lobes; maximum 
cranidial width achieved across rear of posterior border; anterior 
sections of facial sutures subparallel immediately in front of palpe- 
bral lobes, then diverging slightly anteriorly; posterior sections of 
facial suture with strong (ca. 45 degrees from exsagittal plane) 
posterior divergence; anterior margin with strong anterior convex- 
ity; anterior border nearly flat, separated from front of glabella by 
PLATE 1 
83 
abrupt change in slope across trough-like anterior border furrow; 
border and border furrow of even length (sag.; exsag.) medially and 
laterally; axial furrows well impressed posteriorly, subparallel from 
SO to opposite front of palpebral lobe, then diverging anteriorly; 
axial furrows effaced anteriorly opposite anterolateral corner of 
cranidium; preglabellar furrow absent, extent or presence of 
preglabellar field unknown; interocular fixigena large, with only 
weak dorsal convexity; palpebral furrow absent, palpebral lobe flat 
and grading directly into interocular fixigena; palpebral lobe narrow 
(tr.), elongate (exsag.); anterior glabellar furrows effaced; SO shal- 
low but well impressed, of similar length sagittally and exsagittally; 
LO elongate (esp. sag.) and shelf-like, posterior margin with signifi- 
cant posterior convexity; LO and rear of glabella with strong, arcuate 
dorsal convexity; posterior border narrow (tr.), only protruding 
laterally slightly past palpebral lobe; posterior border furrow very 
shallow; entire cranidium with very subdued dorsal sculpture of fine 
pits and small, low, anastomosing ridges. 
Librigena, rostral plate, hypostome, and thorax unknown. 
Pygidium with sagittal length about 60% of maximum width; axis 
with maximum width about 75% of sagittal length; axis occupying 
about 60% of sagittal length of pygidium; anterior margin tranversely 
straight within fulcra, turned sharply posteriorly at fulcrum to run 
distally at about 45 degrees to transverse plane; posterior margin 
subcircular in outline; first pleural furrow defined adaxially to 
fulcrum, shallow but deepest adaxially; all other pleural and 
interpleural furrows completely effaced; articulating half ring very 
short (sag., exsag.); axial furrows extremely shallow, defined mainly 
as a sharp break in slope between pleura and axis, converging gently 
posteriorly, nearly transverse at rear to fully circumscribe somewhat 
blunt posterior of axis; five or six axial rings discernible on internal 
mold, but difficult to discern dorsally; ring furrows transverse and 
shallow on internal mold; entire pleural region lacking dorsal sculp- 
ture; doublure broad, of even width medially and laterally, reaching 
sagittally to rear of axis; relatively strong subparallel doublural 
terrace lines developed and progressively closer spaced on anterior 
half of doublure. 
DISCUSSION. Fortey (1980: 56, 57) described an isolated 
cranidium from what is now recognized as the uppermost Ibexian 
(V,a) of Spitsbergen as ?Protostygina sp. ind. This taxon is very 
similar to and definitely congeneric with P. coronula sp. nov. The 
species are distinguished mainly by the significantly deeper axial, 
anterior border, and occipital furrows of P. coronula. Fortey’s 
suggestion that the Spitsbergen species (and hence the new Irish 
material) is related to P. bohemica (see Horny & Bastl (1970: pl. 8, 
fig. 3) remains the most tenable, despite the distorted internal mold 
preservation of the unique type specimen of that taxon. To the 
extent that evaluation is possible, P. coronula is distinguished from 
P. bohemica particularly by its longer pygidium with much more 
prominent axis. These features distinguish it also from the single 
exfoliated pygidium assigned to Protostygina sp. by Dean (1973; 
Figs 1-6 Nileus sp. 1a-b, It. 25935, cranidium, dorsal and right lateral views, x10. 2a-b, It. 25936, left librigena, external and ventrolateral views, x10. 
3a-c, It. 25937, yolked librigenae-rostrum, anterior, right lateral, and ventral views, x5. 4, It. 25938, hypostome, ventral view, x10. 5a-e, It. 25939, 
dorsal, ventral, and left lateral views, x10. 6, It. 25940, pygidium, dorsal view, x7.5. 
Figs 7-9 Benthamaspis sp. 7a-b, It. 25941, cranidium, dorsal and right lateral views, x15. 8a-b, It. 25943, pygidium, right lateral and dorsal views, x15. 
9, It. 25942, cranidium, dorsal view, x15. 
Figs 10, 13-16 Geragnostus clusus Whittington, 1963 10, It. 25944, cephalic shield, dorsal view, x10. 13, It. 25945, cephalic shield, dorsal view, x15. 
14a-b, It. 25946, enrolled specimen, thoracic and right lateral views, x15. 15a-b, It. 25947, cephalic shield, left lateral and dorsal views, x10. 16, It. 
25948, pygidium, dorsal view, x15. 
Figs 11,12 Ampyx cf. toxotis Fortey, 1975 11, It. 25949, cranidium, dorsal view, x8.5. 12, It. 25950, pygidium, dorsal view, x15. 
Fig.17 Dividuagnostus sp. indet., It. 25951, cranidium, dorsal view, x15. 
