ORDOVICIAN TRILOBITES FROM THE TOURMAKEADY LIMESTONE 
Family TROPIDOCORYPHIDAE Priby!, 1946 
Genus PHASEOLOPS Whittington, 1963 
TYPE SPECIES. Phaseolops sepositus Whittington, 1963, from the 
Cow Head Group (Whiterockian), western Newfoundland, Canada; 
by monotypy. 
DISCUSSION. Whittington (1963) described Phaseolops sepositus 
as the oldest known proetid species, assigning it to the subfamily 
Phacopidellinae Hupé, 1953 (now generally regarded as a synonym 
of Tropidocoryphinae Pribyl, 1946). Hu subsequently (1971) erected 
P. conus, aspecies based upon mis-associated aulacopleurid cranidia 
and tropidocoryphid librigenae and pygidia (seeAdrain & Chatterton 
1995: 310). The taxon is not related to P. sepositus, but rather is an 
aulacopleurid, and will be revised in a forthcoming work by J.M.A. 
The only species subsequently assigned to the genus are P. krafti 
Snajdr, 1983, and Proetus? primulus Barrande, 1872 (see Snajdr 
1983), from the Czech Republic. Neither is adequately known, but it 
is possible that they belong here. 
Owens (1973a: 80, text-fig. 11) considered Phaseolops ceryx to 
represent the oldest and most primitive known proetid, and derived 
P. sepositus from it with question. He subsequently (in Owens & 
Hammann 1990) transferred P. sepositus to the aulacopleuroidean 
family Rorringtontidae. For reasons given below, we consider P. 
ceryx and P. sepositus to be closely related, and to represent the base 
of the radiation of at least the tropidocoryphid proetoids. 
Phaseolops ceryx differs from the Newfoundland type species in 
several obvious respects, but all seem related to effacement. 
Phaseolops ceryx is more similar to younger tropidocoryphids in the 
lack of prominent tuberculate sculpture and the expression of the 
glabellar furrows mainly as shallow, smooth depressions on the 
exoskeleton. Phaseolops sepositus differs from virtually all younger 
taxa in the possession of deep, slot-like glabellar furrows and a 
robust tuberculate sculpture on the preglabellar area and librigenal 
field. The species, however, are almost identical in relative cephalic 
proportions. Particularly striking is the abrupt lateral deflection of 
the anterior section of the facial suture, so that it is held almost 
vertically when the cranidium is oriented with the palpebral lobe 
horizontal (Pl. 15, figs 10b, 11c; cf. Whittington 1963: pl. 5, figs 2, 
5). Also compelling is the size and position of the median occipital 
tubercle. In most subsequent tropidocoryphids, this structure is set at 
more or less half the sagittal length of the occipital ring. In both P. 
ceryx (PI. 15, figs 10a, 11a, 14a) and P. sepositus (Whittington 1963: 
pl. 5, fig. 4), it is set directly at the posterior margin, and actually 
protrudes backward from the margin. We regard these conspicuous 
shared features as synapomorphic, and consider the species, which 
are essentially contemporaneous, to be congeneric. 
Beyond the conventional proetoid morphology of P. ceryx, possi- 
bly a key indicator of the affinities of Phaseolops lies in the thoracic 
structure of P. sepositus. Early tropidocoryphids possess thoracic 
111 
pleural tips in which the pleural furrow shallows abruptly adaxial to 
the tip, and the tip itself is produced laterally as a small, sinuous, 
posterolaterally directed spine. The morphology is perhaps best 
observed in Stenoblepharum (e.g., S. warburgae (Pribyl, 1946), see 
Owens 1973b, fig. 9C), but is present also in species presently 
assigned to Decoroproetus (e.g., D. asellus (Esmark, 1833), see 
Owens 1973b, fig. 4F) and species of Ascetopeltis (e.g., A. bockeliei 
Owens, 1973b, fig. 2A). Exactly the same morphology is seen in P. 
sepositus (Whittington 1963: pl. 5, fig. 1), but not in Rorringtonia, 
which has pointed but not spinose pleural tips (Owens 1981: pl. 1, 
fig. a). In addition, P. sepositus has the general proetoidean thoracic 
segment number of 10, in agreement with all tropidocoryphids, but 
in contrast to the 9 segments seen in Rorringtonia. For these reasons, 
Phaseolops is herein regarded as a tropidocoryphid. 
The genus may prove to be of significance in determining the 
affinities of Proetoidea. The sister taxon of the group is at present 
entirely obscure. If the proposed relationship between Phaseolops 
ceryx and P. sepositus is correct, it is conceivable that the tuberculate 
morphology of the latter, with glabellar furrows deeply incised, is a 
clue to the nature of the sister taxon. Effaced, ‘generalized’ trilobites 
are not unknown in the Ibexian. They are generally assigned to the 
“hystricurines, a group which is at present little more than a 
polyphyletic catchall, and none described thus far share convincing 
apomorphies with the proetoids. The reason for this may be that 
following from the morphology of P. sepositus, the Lower Ordovician 
or Upper Cambrian precursor to the group was a non-effaced, 
tuberculate taxon. Such taxa, including most of the “hystricurines,’ 
are common in the Sunwaptan and Ibexian. Support for this scenario 
lies in the sporadic retention of at least tuberculate librigenae in 
otherwise advanced Ordovician tropidocoryphids (e.g., 
Decoroproetus bodai Owens, 1973b: fig. 4K). 
Phaseolops ceryx sp. nov. 
IAL, 13), eS ©, 7, 95 OZ IAL WS), 
figs 10-14, 18; Pl. 16, figs 1-6 
1973a “Tourmakeady cranidium’, Owens: 80, text-fig. 11. 
1975 Decoroproetus? sp., Fortey & Owens: 229, fig. 1d-If. 
ETYMOLOGY. From the Greek noun keryx, a herald. 
DIAGNOsIS. Glabellar furrows very shallow, nearly effaced; eye 
socle simple and librigenal field lacking sculpture. 
HOLOTYPE. It. 26145 (Pl. 15, fig. 11); paratypes It. 12856, 12857, 
26116, 26117, 26144, 26146-26149, 26153-26158. 
DESCRIPTION. Cranidium with width across midlength of palpebral 
lobes approx. 75% of length (sag.); glabella and LO occupying 75— 
77% of sagittal length of cranidium; glabella with maximum width 
across posterior, approx. equal to length (excluding LO); anterior 
PLATE 16 
Figs 1-6 Phaseolops ceryx sp. nov. 1, It. 26153, cranidium, dorsal view, x27. 2, It. 26154, cranidium, dorsal view, x 33. 3, It. 26155, pygidium, dorsal 
view, X27. 4, It. 26156, transitory pygidium, dorsal view, x40. 5, It. 26157, pygidium, dorsal view, x27. 6, It. 26158, pygidium, dorsal view, x27. 
Figs 7-10, 12-16 Proscharyia platylimbata 7, It. 26159, cranidium, dorsal view, x33. 8, It. 26160, cranidium, dorsal view, x33. 9, It. 26161, holotype, 
cranidium, dorsal view, x33. 10, It. 26162, cephalon, dorsal view, x27. 12, It. 26163, cranidium, dorsal view, x60. 13, It. 26164, pygidium, dorsal view, 
x27. 14, It. 26165, pygidium, dorsal view, x33. 15, It. 26166, pygidium, dorsal view, x40. 16, It. 26167, pygidium, dorsal view, x33. 
Figs 11,20 Celmus michaelmus sp. nov. 11, It. 26168, right librigena, external view, x27. 20, It. 26169, pygidium, posterodorsal view, x33. 
Figs 17-19, 21-23 Dimeropyge? ericina sp. nov. 17, It. 26170, cranidium, dorsal view, x23. 18, It. 26171, cranidium, dorsal view, x33. 19, It. 26172, 
thoracic segment, anterior view, x 27. 21, It. 26173, cranidium, dorsal view, x27. 22, It. 26174, left librigena, external view, x27. 23, It. 26175, left 
librigena, external view, x33. 
Fig. 24 Oopsites hibernicus (Reed in Gardiner & Reynolds, 1909) It. 26176, cranidium, dorsal view, x40. 
All figures are scanning electron micrographs. 
