ORDOVICIAN TRILOBITES FROM THE TOURMAKEADY LIMESTONE 
Thorax unknown. Pygidium (see also Lane 1971: 56) with sagittal 
distance from articulating half ring furrow to rear of medial spines 
44% of maximum width; pygidium composed of three distinct rings, 
pleural segments, and a small subtriangular terminal piece; 
interpleural furrows deeply incised, but first and second ribs fused to 
just over half distance abaxially, second and third ribs fused to about 
two thirds distance abaxially; pleural furrow shallow but incised on 
proximal part of first rib, very faint furrow visible on corresponding 
part of second rib; axial furrow moderately deep opposite first ring, 
progressively shallower posterior, but deepened around small termi- 
nal piece; first axial ring with significant sagittal convexity and 
bowed posteriorly in plan view; second ring less convex and more 
transverse; third ring not inflated and nearly transversely oriented; 
ring furrows shallowed medially; ribs with spatulate, subquadrate 
free tips. 
DISCUSSION. Kawina divergens has previously been known only 
from its holotype pygidium (PI. 7, fig. 2). The species is distin- 
guished from K. scrobiculus (Whittington, 1963) and K. prolificus 
(Billings, 1865) in its less inflated lateral glabellar lobes and 
posteriorly versus anteriorly bowed occipital furrow. It differs from 
K. mercurius (Billings, 1865) in the lack of the autapomorphic 
tranversely impressed S1 of that species. Kawina divergens is quite 
similar to both K. griphus and K. torulus (see generic discussion 
above), but differs from both in the presence of a much finer cephalic 
sculpture and an S1 that is much better impressed proximally to 
more fully isolate L1. The closest comparison among described 
species is with K. arnoldi. Pygidia of the two species are discussed 
above. Shared cephalic features include a similar sagittal convexity, 
similarly subdued dorsal sculpture (although that of K. arnoldi is 
slightly more robust), and similar posterior curvature of SO. The 
species differ particularly in the presence in K. arnoldi of an S1 that 
is strongly sigmoidal in lateral view. 
Genus MAYOPYGE gen. nov. 
TYPE SPECIES. Mayopyge zapata sp. nov., from the Tourmakeady 
Limestone, Co. Mayo, western Ireland. 
OTHER SPECIES. ?Pseudosphaerexochus tuberculatus Warburg, 
1925, Leptaena Limestones, Ashgill, Dalarne, Sweden. and the 
Chair of Kildare Limestone, Ashgill, eastern Ireland (Dean 1971). 
ETYMOLOGY. After Co. Mayo, in which the type locality is situ- 
ated, and the Greek noun pyge, tail. 
DIAGNOSIS. Prominent eye ridge and relatively wide interocular 
fixigena; strong sutural ridge along anterior section of facial suture 
of librigena; swollen knob-like structure proximally on thoracic 
pleura; pygidium with three segments, anterior of which is similar to 
posterior thoracic segment; shallow, ‘v’-shaped anterior pygidial 
doublural margin, with arcuate posterior embayment; densely and 
coarsely tuberculate dorsal sculpture. 
DISCUSSION. The subfamilial affinities of Mayopyge gen. nov. are 
exceptionally difficult to judge. The densely tuberculate dorsal 
95 
exoskeleton is most similar to that developed in many 
acanthoparyphine clades. The prominent peak in convexity at the 
rear of the glabella, seen in many specimens, has obvious compari- 
sons with the hypertrophied structure present in the same topological 
position in species of the primitive acanthoparyphine Nieskowskia 
Schmidt, 1881. Most species of Nieskowskia also have prominent 
tuberculate sculpture. However, Mayopyge lacks any of the 
acanthoparyphine apomorphies. Most importantly, M. zapata dis- 
plays the primitive three-segmented pygidial condition, in contrast 
to the reduction to two segments characteristic of Acanthoparyphinae. 
In addition, the maximum glabellar width in the Irish species is 
achieved across L2, rather than across L1 as in acanthoparyphines. 
Mayopyge does show some similarities to early species of 
Sphaerexochus. The hypostome of M. zapata, for example (Pl. 9, 
figs 17-20), is nearly identical to that of the upper Whiterockian S. 
arenosus (Chatterton & Ludvigsen, 1976, pl. 13, figs 32, 33, 37, 41, 
42). Mayopyge also shares with Sphaerexochus fully isolated L1 
with strong independent inflation. 
In addition to several plesiomorphic features, including its rela- 
tively elongate anterior border and very prominent eye ridge, 
Mayopyge zapata displays several seemingly autapomorphic 
morphologies. The strong inflation of L2 and its near isolation from 
the median glabellar lobe in many specimens (PI. 8, figs 1b, 2c, 9b) 
is not seen in any other species with a strongly inflated glabella. The 
thoracic pleural structure is also apparently unique. In contrast to the 
transverse furrow or row of pits common to most non-cheirurine 
cheirurids, Mayopyge shows only a faint, obliquely inclined furrow 
(Pl. 10, figs la, 2a, 4a), with the anterior pleural band swollen into a 
hemispherical knob and the posterior band greatly reduced. The 
structures seem analogous to those present in Cheirurinae, but in that 
taxon both the anterior and posterior pleural bands are swollen and 
the pleural furrow, though obliquely inclined, runs in a direction 
opposite to that seen in Mayopyge. In cheiruines, the pleural furrow 
contacts the axial furrow anteriorly, and runs posterolaterally. In 
Mayopyge, the contact is posterior and the furrow runs anterolaterally. 
In summary, it does not seem possible at present to relate Mayopyge 
with confidence to other cheirurids. Potentially synapomorphic 
comparisons can be made with acanthoparyphines and with 
Sphaerexochus, but additional relevant diversity will probably be 
necessary to resolve the systematic position of the genus. 
Two cranidia from the Ashgill Chair of Kildare limestone, eastern 
Ireland, figured by Dean (1971: pl. 11, figs 1-3, 9, 10) as 
Pseudosphaerexochus? tuberculatus Warburg, 1925, have coarse, 
dense, bimodal tuberculate sculpture. The species also agrees with 
Mayopyge zapata in its unusually well-impressed S2 and S3. Swed- 
ish type material of P. tuberculatus has never been photographically 
illustrated, but Warburg’s (1925: pl. 10) cranidia are densely tuber- 
culate. Pseudosphaerexochus tuberculatus possibly represents a 
species of Mayopyge, to which it is assigned with reservation herein, 
but it could equally prove to be an acanthoparyphine and confirma- 
tion will require more complete material. 
Mayopyge zapata sp. nov. 
Pl. 7, fig. 6; Pl. 8, figs 1-10; 
Pl. 9, figs 1-21; Pl. 10, figs 1-17 
PLATE 8 
Figs 1-10 Mayopyge zapata gen. et sp. nov. la-d, It. 26024, cranidium, dorsal, right lateral, oblique, and anterior views, x7.5. 2a-e, It. 26025, cranidium, 
dorsal, ventral, right lateral, anterior, and posterodorsal views, x10. 3a-b, It. 26026, cranidium, left lateral and dorsal views, x10. 4a-b, It. 26027, 
cranidium, left lateral and dorsal views, x10. 5, It. 26028, cranidium, oblique view, x7.5. 6a-b, It. 26029, cranidium, dorsal and right lateral views, x10. 
7Ta-b, It. 26030, cranidium, dorsal and right lateral views, x10. 8a-c, It. 26031, cranidium, dorsal, left lateral, and anterior views, x10. 9a-b, It. 26032, 
cranidium, dorsal and oblique views, x7.5. 10a-c, It. 26033, cranidium, dorsal, left lateral, and anterior views, x10. 
