1 
ORDOVICIAN TRILOBITES FROM THE TOURMAKEADY LIMESTONE 
relatively wide genal field. New silicified material (Pl. 11, fig. 14a) 
shows a slightly narrower (tr.) glabellar tongue than is typical of O. 
inconnivus, and the librigena (Fortey 1974, pl. 14, fig. 13) has a 
relatively wide genal field. The population seems to be intermediate 
between O. inconnivus and Opipeuter. sp. A, and it is considered 
preferable to term it O. aff. inconnivus. Henderson (1983) described 
O. insignis from Queensland, Australia, based upon rather fragmen- 
tary material. The genal field is like that of O. aff. O. inconnivus. 
Henderson also stated that one thoracic segment carried a long, 
median spine. Fortey’s (1974) reconstruction of O. inconnivus did 
not show such a spine, but was based upon an entire specimen in 
which the thoracic axis was poorly preserved. It seems likely that the 
thoracic segments figured here on PI. 11, figs 16, 20 are this spinose 
segment. 
Family LEIOSTEGHDAE Bradley, 1925 
Genus AGERINA Tjernvik, 1956 
TYPE SPECIES. Agerina erratica Tjernvik, 1956, from the ‘grey 
marly Upper Planilimbata limestone, Lanne, Narke, Sweden; by 
original designation. 
Agerina palabunda sp. nov. Pl. 12, figs 1-15 
ETYMOLOGY. Latin, wandering, referring to the widespread oc- 
currence of the genus. 
HOLOTYPE. Cranidium, It. 26095 (PI. 12, fig. 1); paratypes It. 
26096-26107, 26084, 26085. 
DIAGNOsIs. Glabellar furrows almost entirely effaced, except for 
smooth patch at S1; glabella with clavate form, axial furrows 
strongly bowed inwards; dorsal cephalic sculpture of fine tubercles. 
DESCRIPTION. Cranidium with sagittal length about 60% of maxi- 
mum width across posterior border furrows; width across midlength 
(exsag.) of palpebral lobes two thirds that across posterior border 
furrows; anterior sections of facial sutures strongly divergent 
anteriorly in front of palpebral lobes, reaching maximum divergence 
opposite anterior border furrow, then strongly convergent opposite 
anterior border; posterior sections of facial sutures curving sharply 
immediately behind palpebral lobe to run nearly transversely, curv- 
ing posteriorly around distal extremity of posterior fixigena; anterior 
border short (sag., exsag.), upturned, nearly flat, almost completely 
overhung by glabella medially, with sculpture of two or three linear 
terrace lines running parallel to margin; border lengthening abaxially, 
separated from anterior fixigena by weakly impressed border fur- 
row; glabella moderately inflated, hourglass-shaped, anterior margin 
with gentle anterior convexity, lateral margins with strong lateral 
concavity; glabellar sculpture of dense, evenly distributed fine tu- 
bercles, all of similar size; S1 not incised, reflected as a smooth 
patch free of tuberculate sculpture (Pl. 12, figs 4, 5); anterior 
glabellar furrows indiscernible; anterior fixigena confined to nar- 
row, subtriangular strip; axial furrow very deeply incised, bowed 
PLATE 12 
103 
strongly adaxially beside palpebral lobe; palpebral lobe large, simi- 
lar in length (exsag.) to posterolateral projection of cranidium, held 
in horizontal plane, with dorsal sculpture of dense granules; poste- 
rior fixigena forming relatively long (exsag.) transverse strip, 
sculpture of fine tubercles similar to that of glabella; posterior 
border furrow similar in depth to axial furrow, of similar length 
medially and laterally, running nearly exactly transversely; posterior 
border relatively short proximally, lengthening and becoming slightly 
lobate laterally, with considerable exsagittal dorsal convexity; SO 
with gentle posterior curvature, similar in depth and incision to axial 
furrow and posterior border furrow; LO with posterior margin de- 
scribing very shallow ‘“W’ shape so that sagittal length is slightly 
shorter than nearby exsagittal length, then shortening considerably 
behind L1; LO with tuberculate sculpture similar to that of anterior 
part of glabella, no distinct median node discernible, with moderate 
sagittal convexity. 
Librigenal field with anterior width (tr.) 60-65% of maximum 
width just behind eye; maximum width about 55% of maximum 
length (exsag.); lateral border broad, slightly wider posteriorly than 
anteriorly, with prominent, rounded, dorsal inflation, sculpture of 
about nine coarse terrace lines, arranged subparallel to lateral mar- 
gin anteriorly, running back to intersect margin posteriorly, more 
closely spaced near lateral margin, slightly anastomosing with some 
merging and disappearance of individual lines; lateral border furrow 
deep, narrow, shallowing abruptly posteriorly in front of genal spine; 
lateral border furrow and lateral margin with strong lateral curva- 
ture; genal spine long and tapering, terrace lines of lateral border 
continued along length without interruption; only small portion of 
posterior border developed on librigena, beside strong sutural 
embayment for posterolateral part of cranidium; field with gentle 
dorsal convexity, sculpture of fine tubercles, slightly coarser adaxially 
and beneath eye; prominent eye socle of single continuous, narrow 
band; eye large, with length (exsag.) slightly more than double width 
at midlength; doublure nearly flat, with subdued terrace lines devel- 
oped mainly near lateral margin, much finer than those on dorsal 
aspect of lateral border. 
Rostral plate subrectangular in anterior aspect, connective sutures 
longer than rostral suture; terrace lines of anterior librigenal projec- 
tions continued across plate without interruption; connective sutures 
converging ventrally, nearly meeting posteriorly on strongly curved 
ventral part of plate. 
Thorax unknown. Pygidium with sagittal length 50-55% of maxi- 
mum width; wide, gently tapering and obtusely rounded axis slightly 
less than half pygidial width (as shown on best silicified specimen, 
Pl. 12, fig. 14a); axis extends close to border, in contact via narrow 
postaxial ridge; five narrow (tr.) axial rings extending to postaxial 
ridge; posteriormost ring may be obscure; gently convex pleural 
fields show two defined segments, only the anterior pleural furrows 
are at all deep; border is narrow and distinctly convex, and carries a 
sculpture of a few raised lines like those on the genal border; 
doublure recurved ventrally and wider than border, showing an 
anterolateral articulatory ‘tooth’ (cf. Annamitella Fortey & Shergold 
1984, pl. 38, fig. 15). 
Figs 1-15 Agerina palabunda sp. nov. 1a-c, It. 26095, holotype, cranidium, dorsal, anterior, and left lateral views, x15. 2a-d, It. 26096, cranidium, 
dorsal, ventral, anterior, and right lateral views, x15. 3a-d, It. 26097, cephalon, dorsal, ventral, left lateral, and anterior views, x15. 4, It. 26098, 
cranidium, dorsal view, x15. 5a-b, It. 26099, cranidium, dorsal and left lateral views, x15. 6, It. 26100, cranidium and left librigena, dorsal view, x15. 7, 
It. 26101, right librigena, external view, x15. 8, It. 26102, right librigena, external view, x15. 9, It. 26103, right librigena, external view, x15. 10, It. 
26104, right librigena, external view, x15. 11a-b, It. 26107, left librigena, external and internal views, x15 and x10. 12, It. 26105, left librigena, external 
view, x15. 13, It. 26106, left librigena, external view, x15. 14a-b, It. 26084, pygidium, dorsal and ventral views, x10. 15, It. 26085, pygidium, dorsal 
view, x10. 
