Pseudoolenoides fossilmountainensis, Adrain & Karim, 2012

Adrain, Jonathan M. & Karim, Talia S., 2012, 3467, Zootaxa 3467, pp. 1-97 : 30-35

Pseudoolenoides fossilmountainensis n. sp.

Plates 21–27

Material. Holotype, cranidium, SUI 130061 (Pl. 22, figs 1–3, 5, 7), and assigned specimens SUI 130062–130110 , from Section K-South 152.4 T m and 159.7 T m, Kanosh Formation (Darriwilian; Pseudoolenoides fossilmountainensis Zone ), southern Confusion Range , Ibex area Millard County, western Utah, USA.

Etymology. From Fossil Mountain.

Diagnosis. Glabella with fine, scattered tubercles with distinct backwardly-raked, subtriangular shape; glabella narrow anteriorly; pygidium with distinct laterally flared border protruding from tagmatized region behind fourth pleural spine; posterior pygidial region narrow, not tapering broadly into posteromedian spine base.

Description. Cranidial measurements were made on the most complete specimens of Pl. 21–23. Measurements were doubled from the sagittal line if necessary, e.g., for specimens with a single intact posterior projection. Cranidium moderately vaulted (sag., tr.), broad and fairly long, with maximum width across palpebral lobes (δ) 135.2% (127.1–140.1%) sagittal length, width across β 112.0% (103.6–117.3%) length, width across Ύ 103.7% (96.0–115.3%) length, width across Ɛ 104.4 % (92.5–119.8%) length, and width across posterior projections 128.2% (124.1–132.8%) length, with sculpture of anastomosing ridges running generally subparallel to axis, slightly posteromedially directed, sculpture more scrobiculate toward anterior and lateral edges of cranidium; anterior branch of facial suture moderately laterally bowed along frontal areas, slightly anterolaterally bowed along lateral parts of anterior border; posterior branch of facial suture very short (obliquely), extends posterolaterally, but only to even with palpebral furrow; anterior border short, longest medially, particularly anterior to pits at anterolateral corners of LF, laterally tapered, broad, but narrower than fixigena, broadly and unevenly anteriorly bowed, with median section breaking arc of curve with nearly transverse anterior margin, median section gently anteriorly downturned, lateral sections roughly horizontal, border with sculpture of very fine anastomosing ridges roughly parallel to curvature; doublure very slightly turned under medially, but just a rim, mainly exposed as anterior face of border, with fine transverse ridge sculpture; anterior border furrow short, moderately deep, arcuate like border laterally, overlying preglabellar furrow medially and more strongly and narrowly anteriorly bowed, also slightly shallower medially, convergent with axial furrows in small, deep pits; frontal areas large, long, fairly wide, narrower posteriorly, trapezoidal, with posterolaterally slanted anterior and posterior margins, gently anteriorly bowed along mid-length and anteroventrally sloped at about 30–35º angle from horizontal (lateral view), with small, ovoid swelling located adjacent to axial furrow and ocular ridge, reflecting position of fossula on ventral surface, and with sculpture of anastomosing ridges forming small polygons overlain by short scrobiculate ridge situated at about 1/4 length of frontal area, scrobiculate ridge sloped posterolaterally at about 30–35º from horizontal, slightly steeper than anterior border furrow, steeper abaxially, intersects cranidial margin at β, stops short of intersecting axial furrows near their junction with anterior border furrow, polygonal sculpture of frontal areas smaller anterior to ridge and more equant, more elongate posterior to ridge; ocular ridge moderately inflated, lower ad- and abaxially, directed posterolaterally from just anterior to S3 to palpebral lobe at about 30–35º below horizontal; palpebral lobes relatively small in proportion to cranidium, slightly greater than semicircular in area, strongly laterally bowed, but unevenly arcuate, with posterior end closer to sagittal axis, lobes with broad, slightly more inflated lateral margin, margin wider and longer from midlength of lobe posteriorly, tapered far posteriorly, shorter/narrower anteriorly into connection with ocular ridge, lobes elevated to roughly half height of glabella, with lateral edge slightly ventrally bent (anterior view), lobes also anteroventrally sloped (lateral view), and with anastomosing line sculpture differentiated from that of fixigenae by forming small polygons; palpebral furrow best expressed on small specimens (e.g., Pl. 22, fig. 1), short and narrow, shallow, shallowest along mid-course (midlength of palpebral lobe), course strongly laterally bowed, "U"-shaped, arc of curve uneven (extends further anteromedially), furrow connects anteriorly to shallow furrow along posterior edge of ocular ridge, stops abruptly posteriorly at edge of lobe; interocular fixigena trapezoidal, broad and fairly long, with posterolaterally sloped anterior margin due to strike of ocular ridge, roughly horizontal, only slightly anteroventrally sloped, with far abaxial section slightly raised toward palpebral lobe (anterior, lateral views), with sculpture like that of posterior part of frontal areas (continuous across ocular ridge), and with narrow, short, crescentic slight swelling across from L1 (more prominent on smaller specimens, e.g., Pl. 22, figs 1–3) surrounding small, depressed alae; posterior fixigena very short and relatively wide, rectangular except for lateral extension of posterior margin along posterior projection, strongly posteroventrally sloped (lateral view), with sculpture like that of interocular fixigena; posterior border furrow short, nearly effaced adjacent to glabella and shallow adaxially, much deeper abaxially starting at about half-width, but abruptly effaced just short of cranidial margin, course nearly transverse, very shallowly posterolaterally angled; posterior border narrow, with distance across posterior projections less than distance across palpebral lobes, border short, not quite as long as anterior border, very slightly longer adjacent to LO than at lateral tip, moderately inflated, with shallow furrow (most apparent adaxially and far abaxially) along posterior margin for articulation with thorax, with sculpture like that of fixigenae but a little more effaced; doublure very short, just a rim curled underneath posterior margin, slightly longer far abaxially; axial furrows moderately wide, of varying depth, deepest along L1, shallower posteriorly and anteriorly until deeper again along LF, gently anteriorly divergent until mid-length of glabella, then bowed laterally around L2 and L3, then more strongly anteriorly convergent toward junction with anterior border furrow; glabella with distinct L1 and less distinct L2 and L3, overall elongate and fairly narrow, with maximum width across L2 (even with inner end of ocular ridge) 73.7% (68.7–78.6%) sagittal length excluding LO, bullet-shaped, with strongly tapered and bowed anterior end and straight-sided posterior end (along L1; gently laterally expanded along L2 and L3), strongly transversely vaulted posterior to mid-length, less vaulted anteriorly, moderately strongly sagittally vaulted, with sculpture of fine anastomosing ridges, ridges form rough, strongly anteriorly bowed concentric arcs with subparallel lateral segments, ridges overlain by small, posteriorly-raked, triangular tubercles, tubercles concentrated medially; L1 broad, short adaxially and elongated abaxially, moderately independently inflated, with fine scrobiculate ridge on anterior margin leading into S1, ridge stops after half-width of lobe but before meeting axial furrow; S1 very long and shallow adaxially, short and deep abaxially, extends far adaxially but just separated from axial furrows by very narrow ridge of raised glabella running from L1 to L2 (shown well on Pl. 21, figs 1, 9), strongly anterolaterally directed; L2–LF and sulci poorly defined on all but smallest specimens (e.g., Pl. 22, fig. 1), L2 and L3 very weakly independently inflated; L2 (as defined by furrows) wedge-shaped, very short near axial furrows, with wide posterior margin along S1 and narrow anterior margin along S2, lobe generally posteromedially directed; L3 very short and narrow (as defined by furrows), anteromedially directed; S2 and S3 short and narrow, barely extend out of axial furrows, shallow, anteromedially directed, S3 located at median end of ocular ridge, S2 located halfway between lateral ends of S3 and S1; LF very large, long and fairly wide, strongly anteriorly tapered, decreasingly convex (tr.) anteriorly; LO moderately inflated, wide, with width across junction of axial furrows and posterior margin 49.7% (44.5%–53.7%) sagittal cranidial length, lobe short laterally, rounded longer extension medially creating wavy anterior margin, LO 16.1% (14.5–17.5%) sagittal length of cranidium at maximum, with evenly arcuate posterior margin, and with sculpture of anastomosing ridges anteriorly, connected to SO ridges, fewer ridges posteriorly on lobe, with small median node situated even with lateral anterior margin (so at slightly anterior to half length medially), and with triangular backwardly-raked tubercles like those of glabella concentrated medially on most specimens; doublure long medially, reaches posterior margin of SO, strongly tapered and short laterally, with shallowly "W"-shaped anterior margin, slightly raised posterior rim, and sculpture of very fine transverse ridges; SO moderately deep, deeper abaxially, long, with roughly transverse anterior margin and shallowly "W"-shaped posterior margin, crossed by ridges of anastomosing, but generally axis-parallel sculpture medially, and with weaker anastomosing sculpture laterally.

Rostral plate unknown.

Hypostomal measurements were made on specimens of Pl. 24–25. Hypostome broad and relatively long, with maximum width across anterior wings 109.2% (106.8–114.0%) sagittal length, with sculpture of fine, closely spaced anastomosing ridges on middle body and more curvilinear fine ridges on borders and doublure; hypostomal suture very shallowly "W"-shaped, gently anteriorly bowed medially, and anteriorly recurved far laterally; anterior border of a very short, inflated rim, with short, shallow furrow behind it; anterior wings triangular, very large, strongly upturned, with anterolateral margin steeply posterolaterally sloped away from anterior border, and with raised rim on posterior margin leading into lateral border, effaced except for a few fine ridges near anterolateral margin and fine ridges following curvature of raised posterior margin; middle body ovoid, elongate and fairly narrow, with width at lateral notch 78.6% (76.1–82.1%) sagittal length, distinctly divided into anterior and posterior lobes by short middle body furrow with strongly posteromedially directed course; furrow discontinuous medially and confluent with lateral border furrow along anterior wings, depth of furrow slightly irregular, with pitted appearance, shallowed at lateral notch where posterior lobe of middle body pinches out; anterior lobe of middle body moderately ventrally inflated (sag., tr.; most of transverse convexity of hypostome due to large anterior wings), ovoid, with lateral bounds undefined by furrow along wings, demarcated instead by effacement of wings vs complex anastomosing ridge sculpture of middle body (as well as change in slope onto wings), sculpture forms small polygons anteromedially, larger, wider polygons medially with more transverse ridges, fewer polygons and more ridges posteriorly, and more widely spaced ridges running approximately parallel to sagittal axis anterolaterally; posterior lobe broadly crescentic, about 1/3 length of anterior lobe at medial maximum, anterolaterally tapered, pinched out at lateral notch, moderately strongly inflated, slightly higher laterally than medially, with sculpture of fine anastomosing ridges roughly transversely directed across lobe, connects to sculpture of anterior lobe and lateral and posterior borders; maculae small, ovoid, positioned just posterior of inner end of middle body furrow, effaced and raised slightly above anterior edge of posterior lobe, less noticeable on larger specimens; lateral border furrow short and deeply impressed along posterior margin of anterior wings (where confluent with middle body furrow), slightly anterolaterally but almost transversely directed along wings, much shallower and curved posterolaterally around lateral notch, then very shallow, narrow, and gently posteromedially directed along posterior lobe of middle body; lateral border very narrow, just an inflated (strongest at lateral notch), downturned rim with fine ridges running parallel to length, with pair of small, finely tapered and pointed spines at shoulders; posterior border furrow arcuate, strongly posteriorly bowed, forms smooth arc in most specimens, but deflected around median projection of posterior lobe of middle body in some (e.g., Pl. 24, figs 1, 15), deep medially and far anterolaterally, shallower between these points (across from base of posterior border spines), meets shallow lateral border furrow about halfway between shoulder and posterolateral corner; posterior border slightly inflated, highest posteromedially on very short part of border, longer and less inflated exsagittally, merging into triangular base of two pairs of spines similar to those of lateral border at posterolateral corners, spines triangular and somewhat dorsoventrally flattened, but with narrow ridge running anteroposteriorly down longer, slightly thicker adaxial spine, abaxial spine much shorter and narrower, border with sculpture of fine, concentric, semi-anastomosing ridges following contours of border; doublure of lateral and posterior borders narrow and short respectively, dorsomedially upturned, with small, triangular posterior wings at posterior end of very deep (considered from anterior side), fairly long lateral notch, doublure widest and longest at posterolateral corners over bases of spines, reaches posterior border furrow, with sculpture of roughly concentric fine ridges.

Librigenal measurements were made on the most complete specimens of Pl. 23. Librigena of small main body and large genal spine; anterior branch of facial suture very long, approximately equally split along field and along anterior projection of lateral border, very steeply sloped along field, gently anteromedially curved along border, cuts border such that anterior face of doublure is exposed in triangular slice, sections form approximately 125º angle at border; posterior branch of facial suture extremely short, extends only along eye and across posterior border; visual surface composed of numerous tiny, closely packed lenses (more clearly seen ventrally), reniform, long and moderately wide, tall, with rounded dorsal surface and steeply sloped lateral surface (ventrolateral view); circumocular furrow strongly posterolaterally curved, moderately narrow, deep, incised; librigenal field small, trapezoidal, narrow and fairly short, with narrowest width under midlength of eye 32.6% (27.6–37.3%) exsagittal length of field along lateral border furrow, gently laterally convex, with densely spaced anastomosing line sculpture (e.g., Pl. 23, fig. 16) or scrobiculate sculpture (e.g., Pl. 23, fig. 6), and with distinct raised, semianastomosing ridge cutting across field from about mid-width of anterior edge to mid-width of posterior edge (diagonal and closer to eye posteriorly due to wider anterior edge); lateral border furrow narrow and fairly deep (shallower on some, e.g., Pl. 23, figs 14, 17–19), shallower posteriorly, only very slightly laterally bowed (moreso posteriorly), separated from posterior border furrow by swollen base of genal spine, includes sculpture of field; lateral border moderately inflated, dorsoventrally flattened into bluntly bladed edge, fairly narrow, narrower anteriorly, anterior projection almost equal in length to remainder of border, with shallowly curved rostral suture at tip (Pl. 23, figs 6, 16, 17), projection gently anteroventrally curved (ventrolateral view), whole border with chevron-shaped ridge sculpture, vertices of chevrons roughly at half width of border, more adaxial anteriorly onto projection and pointed anteriorly, sculpture continuous with, but more anastomosing than, similar sculpture of genal spine, border merged into base of spine; genal spine with similar inflation as lateral border, but less flattened, with ovoid cross-section, base slightly more inflated than librigenal field, spine moderately wide, gradually posteriorly tapered, incomplete on all specimens, but very long, at least 343.2% length of field (Pl. 23, fig. 11), with chevron line sculpture, vertices located at lateral margin posteriorly, move adaxially anteriorly and onto lateral border, ventral sculpture of posteromedially sloped diagonal lines continuous with abaxial branches of dorsal sculpture; posterior border furrow short and deep, longer and deepest adaxially, nearly perpendicular to lateral border furrow, much shallower and curved along base of spine on field; posterior border moderately short, narrower than length of lateral border (excluding anterior projection), reaches to approximately mid-width of eye (separated by overlapping section of posterior border and circumocular furrows), tapered far laterally around base of genal spine and merged onto spine, nearly effaced, with faint ridges roughly parallel to anterior margin; doublure wide laterally, reaches lateral border furrow, raised such that border has ovoid cross-section, with sculpture of subparallel ridges following arc of border and merging into dorsal sculpture of border and spine, shorter posteriorly, and tapered adaxially, effaced or with faint ridge sculpture near posterior edge, with very small Panderian notch expressed mainly as slightly swollen rim located almost at ω.

Total number of thoracic segments unknown, at least six present (Pl. 27, fig. 22). Thoracic measurements were made on specimens of Pl. 25. Thoracic segments fairly shallowly vaulted, axis more vaulted than pleurae, with moderately narrow axis and broad pleurae, axial width 47.1% (43.2–50.3%) width across anterior pleural band; articulating half ring short, a little shorter than axial ring, laterally tapered, with anastomosing line sculpture posteriorly; articulating furrow of varying length and depth (likely from position in thorax), short and deep (e.g., Pl. 25, fig. 17) to long and shallow (Pl. 25, fig. 9), shorter laterally, course posteriorly bowed to very shallowly "W"-shaped, with line sculpture roughly parallel to sagittal axis concentrated medially, extends anteriorly onto posterior part of articulating half ring and posteriorly onto anterior face of axial ring as more transversely oriented lines; axial ring moderately inflated, higher medially, fairly short, shallowly arcuate, longer laterally near axial rings, with sculpture of small tubercles, points of tubercles raked posteriorly, and of fine ridges near anterior margin, swept back posterolaterally on some specimens (e.g., Pl. 25, fig. 1); doublure similar to that of LO, with shallowly "W"-shaped anterior margin, long medially, reaches to articulating furrow, sharply tapered and very short laterally, with very fine transverse ridge sculpture; axial furrows narrow, moderately deep, subparallel to slightly anteriorly divergent, with tips tucked around margins of ring; inner pleurae broad, about twice as wide as outer pleurae (excluding spine), horizontal; outer pleurae sloped ventrolaterally from fulcrum at about 55–60º below horizontal; anterior and posterior pleural bands of approximately equal short lengths, both effaced on most specimens (but see Pl. 25, fig. 9); anterior band with extremely short articulating ridge on inner pleurae defined posteriorly by fine furrow, and with small, sharp, triangular articulating facet near ventral margin; pleural furrow long and shallow, shorter at ad- and abaxial ends, course roughly transverse to gently posterolateral, with sculpture of fine ridges roughly parallel to sagittal axis; posterior pleural band with margin of inner pleurae turned ventrally to articulate with ridge on anterior band of other segments, with small posterior bulge near fulcrum; pleural spine formed from both pleural bands, triangular, fairly long adaxially, anterior margin curved and strongly posteriorly tapered, posterior margin less strongly tapered, spine gently slopes ventrolaterally from base just above ventrolateral margin of segment with tip below margin of segment, with sculpture of fine ridges following shape of spine; pleural doublure not present on anterior margin of inner pleurae, only a rim on posterior margin of inner pleurae, very narrow laterally near base of spine, just curled in dorsomedially as a rim.

Pygidial measurements were made on the best preserved specimens of Pl. 26–27. Pygidium composed of four distinct axial rings with spinose pleurae, with fifth ring lacking pleural spines more weakly expressed on most specimens, and sixth–seventh rings visible on some (e.g., Pl. 26, fig. 2, Pl. 27, figs 1, 3, 4), and with very small terminal piece, pygidium moderately vaulted (sag., tr.), main body broad and strongly posteriorly tapered, with maximum (excluding spines) width across first segment 154.6% (137.9–169.8%) sagittal length excluding articulating half ring and spine; articulating half ring short, tapered laterally, lens-shaped; articulating furrow fairly short, shallower anteriorly and deeper posteriorly, transverse to gently posteriorly bowed in course, with fine ridges parallel to axis crossing furrow onto articulating half ring; axis moderately strongly vaulted, lower posteriorly, long, 87.3% (82.4–96.0%) sagittal length of main body (both measurements excluding articulating half ring), broad anteriorly, with width across first axial ring 48.4% (46.5–51.2%) width across first segment, strongly posteriorly tapered, with sixth ring approximately 1/3 width of first ring and fourth ring 64.3% (62.0–68.8%) width of first ring; axial rings independently inflated, but first four much more distinctly so than subsequent rings, first 4–5 rings short medially, much longer exsagittally, with anteriorly bowed posterior margin and more gently posteriorly bowed median anterior margin, subsequent rings with transverse margins, ring sculpture of small and moderately large tubercles medially, with ridges subparallel to sagittal axis (some more transverse) connecting tubercles, ridges become posterolaterally angled far laterally; inter-ring furrows deep, deeper exsagittally near axial furrows, very long, with anteriorly bowed anterior margin, possibly include poorly differentiated pseudo-articulating half rings, furrows with sculpture similar to that of thoracic ring furrows, with ridges running roughly parallel to sagittal axis crossing furrows and running onto rings, but discontinuous over rings, also with some anastomosing ridge segments; sliver-like terminal piece posterior of axial rings 5–7 (shown well on specimens of Pl. 27; posterior rings weakly defined by shallow inter-ring furrows and transverse lines of tubercles on crest of rings); posterior margin of axis poorly posteriorly defined by post-axial furrow, with weakly inflated median ridge leading onto posterior spine in some specimens (e.g., Pl. 26, figs 1, 2); axial furrows moderately wide, slightly wider anteriorly, deep, much shallower far anteriorly over first segment and posteriorly along rear of axis, course strongly anteriorly divergent; posterior furrow weakly expressed in most specimens (but see Pl. 26, fig. 11, Pl. 27, fig. 3), strongly posteriorly bowed, very short, moderately–very shallow; pleurae moderately long, slightly longer than corresponding axial rings, maximum length of pleurae on first segment 25.9% (22.2–31.2%) sagittal length of pygidium, pleurae moderately narrow, about half width of axis, with relatively broad, transverse inner pleurae, sharp fulcral angle of about 120º, and narrower, strongly laterally downturned outer pleurae, pleurae mainly effaced, with a few granules and segments of fine ridges, with anterior and posterior bands of approximately equal length, bands increasingly posterolaterally directed posteriorly, merged and indistinct along rear of axis, tapering posteriorly into base of posterior spine; anterior pleural bands longer abaxially, slightly broader than corresponding posterior band, moderately inflated, more strongly inflated than posterior bands, with short articulating tongue (inner pleurae) and triangular flange (outer pleurae, anterolateral edge of lateral border) on first segment; pleural furrows long, moderately deep, shorter and deeper exsagittally on outer pleurae, with sculpture of fine, closely spaced, partially anastomosing ridges running roughly perpendicular to gently posterolateral course of furrow; posterior pleural bands similar to anterior bands, but longer adaxially and less inflated; interpleural furrows mostly effaced, very short (Pl. 26, fig. 2), shallow, increasingly posterolaterally directed; pleural spines on first four segments, posterolaterally curved, blade-like, dorsoventrally flattened with distinct anterior and posterior edges, spines as long as pleurae adaxially, gradually tapered to blunt point at posteriorly- or posteromedially-directed tip, a little broader (oblique) than pleurae, with sculpture of fine, semi-anastomosing ridges running mostly subparallel to curvature of spines on dorsal surface, and fewer, very fine ridges concentrated near edges on ventral surface; slightly widened and very slightly flattened, bluntly laterally curved area of merged pleurae just posterior to fourth spine; posterior spine conical, long, full length unknown; at least 125–126% length of main body (Pl. 27, fig. 1), moderately wide, gradually posteriorly tapered, raised about 15º above horizontal, with fine ridge sculpture shaping very closely spaced inverted chevrons dorsally and chevrons ventrally, individual ridges connected laterally; pygidial border expressed mainly ventrally along sides of pygidium, also partially visible posteromedially in posterior view along rear of axis, forms moderately narrow, inflated rim with subparallel ridge sculpture, merged posteromedially into ventral base of posterior spine, anterior tips turned out laterally into articulating flange on anterior pleural band of first segment; pygidial doublure held subvertically, only visible anteriorly (Pl. 26, fig. 18), short, slightly longer medially and slightly anterolaterally tapered, with fine ridge sculpture like that of border.

Ontogeny. Cranidia of P. fossilmountainensis (cf. Pl. 21, fig. 1, Pl. 23, fig. 1) become broader overall; the anterior part of the cranidium (in front of the ocular ridges) becomes longer relative to the posterior part; anastomosing ridge sculpture overall becomes finer and a little more widely spaced; the anterior border shortens, especially medially; all cranidial furrows (except S1) become shallower; the anterior branch of the facial suture becomes longer and more weakly laterally bowed; the fixigenal bosses above the fossulae become more prominent; the eye ridges become relatively shorter and a little less inflated; the palpebral lobes become smaller, with wider, less inflated rims; the glabella broadens and inflates; S1 deepens and lengthens, and the scrobiculate sculpture of the posterior rim develops; glabellar tuberculation develops anteriorly, becomes more densely spaced overall; individual tubercles shrink in size and become posteriorly raked; anastomosing ridge sculpture develops on the glabella; SO lengthens; LO shortens a little and the anterior margin becomes "W"-shaped; and the median LO node becomes smaller, but not less prominent.

The hypostome (cf. Pl. 24, figs 3, 15) broadens overall; all furrows become shallower; the sculpture becomes finer and more closely spaced; the posterior lobe of the middle body shortens; the middle body overall becomes less inflated, and the posterior lobe becomes particularly less independently inflated; the lateral border spines at the shoulder shrink to nubs and those at the posterolateral corners become shorter; and the posterior border spines become shorter and narrower.

Librigenal ontogenetic changes (cf. Pl. 23, figs 3, 16) include enlargement of the eye (it becomes distinctly wider, although not relative to the size of the librigenal field), while the individual lenses become smaller; the circumocular furrow shallows and widens; the librigenal field shortens and broadens; the scrobiculate ridge sculpture on the field develops and strengthens; the anastomosing ridge sculpture of the field develops; the lateral and posterior borders inflate slightly; and the anterior projection of the lateral border lengthens relative to the field.

The thorax is not sufficiently well known to evaluate most ontogenetic changes, but comparison of the thoracic segments attached to the juvenile thoracopygidium (Pl. 27, fig. 22) with individual segments (Pl. 25) shows that the tuberculate sculpture of the axial ring becomes more densely distributed and the tubercles grow into the characteristic posteriorly-raked form.

Pygidial ontogenetic changes (cf. Pl. 26, figs 1, 14, Pl. 27, figs 15, 24) include overall broadening of the main body; median shortening of the axial rings; the first four inter-ring furrows lengthen, particularly the first one, but the fifth shortens; the ring furrows become shallower medially and deeper laterally; the rear of the axis lengthens and narrows; axial ring tubercles become less prominent; anastomosing ridge sculpture becomes more prominent; pleural furrows lengthen and deepen; and the median posterior spine becomes relatively thinner.

Discussion. Pseudoolenoides fossilmountainensis is closely similar to P. carterensis , and is compared in detail with that species below.