786


Journal of Paleontology 91(4):781–798


proximal edge; large, prominent spine articulations not sunken into depressions and bearing conical, pointed arm spines exceeding the length of an arm segment.


Occurrence.—Coln Quarry, Lechlade, Gloucestershire, UK 51.6951ºN, 1.7372ºW; ex situ layer of fissile gray shaley clay from the jason Zone, Peterborough Member, lower Oxford Clay, Callovian, late Middle Jurassic.


Description of holotype.—EE 16205 (Fig. 3) is an articulated disk (4.58mm disk diameter) exposing both dorsal and ventral sides and with proximal segments of one arm preserved; ventral side covered by an arm fragment comprising eight median to distal segments and belonging to the holotype or to another specimen of the same species; dorsal side of the disk covered in its central part by few small, round, imbricate and moderately thick scales and a slightly larger circular central primary plate; remaining dorsal side of the disk covered by large, rounded isosceles-triangular radial shields (Fig. 3.2) accounting for approximately two-thirds of the disk radius joined in pairs over their entire length and separated interradially by a single plate similar in shape to the radial shields but slightly narrower; no removable granules or spines or conspicuous stereom orna- mentation discernible on the dorsal disk plates and scales. Ventral side of disk with relatively few interradial scales


similar in shape and size to the dorsal disk scales, devoid of removable granules or spines. Genital slit extending over at least half of the disk radius; no genital papillae discernible; abradial genital plate (Fig. 3.4) length approximately four times width, with longitudinal ridge but devoid of perforation on exposed side. Oral shield (Fig. 3.3) arrow-shaped, with pointed, acute proximal angle, concave lateral edges, and rounded rectangular distal portion; adoral shields (Fig. 3.3) comparatively broad, with wide distal portion encompassing almost half of the second oral tentacle opening; proximal tips of adoral shields meeting in front of oral shield; second oral tentacle pore (Fig. 3.3) opening inside mouth slit; oral plates stout and wide; first ventral arm plate radially compressed pentagonal, wider than long, with obtuse distal angle, pointed lateral angles, and rounded rectangular proximal edge; lateral oral papillae (Fig. 3.3) fully separated but contiguous, rounded rectangular except for pointed distal-most papilla, second distal-most papilla largest, remaining papillae continuously decreasing in size toward the dental plate; single, short, conical apical oral papilla, slightly smaller than neighboring lateral oral papillae; teeth not exposed. Only proximal arm segments preserved (note that the


median to distal arm portion covering the ventral side of the holotype is ignored here as it might well belong to another individual), segments nearly as long as wide; LAPs with weak constriction and coarsely meshed outer stereom with slightly enlarged trabecular intersections; spine articulations on elevated part of distal LAP portion, at some distance from the distal edge of the plate; spine articulations (Fig. 3.7) relatively large, evenly distributed over the entire distal portion of the LAP, with a dorsalward increase in size of the spine articulations and in the distance separating them; dorsal-most spine articulation visible in dorsal view; spine articulation composed of a large round muscle opening proximally bordered by a thin, irregularly denticulate vertical ridge and distally encompassed by a wider,


more strongly protruding, smooth, semicircular and oblique vertical ridge; nerve opening slightly smaller than muscle opening, distally bordering the semicircular ridge; arm spines (Fig. 3.6) conical, pointed, with rough longitudinally reticulate outer surface, slightly longer than one arm segment; ventral edge of lateral arm plates with deep tentacle notch, distally encompassed by a thinned ventro-distal edge of the lateral arm plate. Ventral arm plates (Fig. 3.5) widest distally, with straight distal edge, deeply concave latero-proximal edges, and pointed proximal tip, separated by lateral arm plates on all exposed segments; tentacle openings large, covered by two oval, nearly equal-sized tentacle scales, developed as between-plate open- ings in all preserved arm segments. Dorsal arm plates (Fig. 3.6) small, fan-shaped, with right proximal angle and convex distal edge, widely separated by lateral arm plates.


Paratype supplements.—EE 16206 (Fig. 4.1) is an articulated disk (4.63mm disk diameter) exposing both ventral and dorsal sides; ventral disk morphology well in agreement with that of holotype; dorsal disk plating better preserved than in holotype, with clearly radial shield pairs abutting over their entire length interradially separated by a single plate similar in size and shape to radial shields. EE 16207 (Fig. 4.2) is an articulated armfragment composed


of seven proximal to median segments; proximal segments similar to those of holotype; median arm segments becoming progressively more elongate; median LAPs without constriction and with smaller and less prominent spine articulations; arm spines of median segments as long as half an arm segment; tentacle pores large and developed as between-plate openings in two proximal-most segments; tentacle pores of the following segments developed as within-plate perforations, strongly decreasing in size and progressively moving from a ventral to a ventro-distal position toward the distal-most preserved segment; proximal-most within-plate tentacle perforation with two oval scales; following tentacle openings with no discernible scales; ventral armplates strongly decreasing in size fromproximal-most to distal-most preserved segment; the two proximal-most ones similar to those observed on holotype, the following ventral arm plates fan-shaped, wider than long. EE 16208 (Fig. 4.3) is an articulated arm fragment


composed of nine proximal to median arm segments; proximal ones similar to those of holotype, median ones more elongate; median LAPs devoid of constriction but with similar outer surface ornamentation as proximal lateral arm plates; dorsal- most spine articulations decreasing in size and moving from a nearly dorsal to a lateral position from the proximal-most to the distal-most preserved segments; arm spines of median segments equaling half the length of an arm segment; dorsal arm plates discernible on all preserved arm segments. EE 16209 (Fig. 4.4), EE 16210 (Fig. 4.5), and EE 16211


(Fig 4.6) are dissociated proximal, median, and distal LAPs, respectively; rounded rectangular outline; proximal LAP nearly as long as high, distal one approximately 1.5 times wider than high; dorsal edge weakly concave, distal edge straight to very weakly convex; proximal edge deeply concave, devoid of discernible spurs but paralleled by deep, poorly defined furrow; weak horizontal striation near central part of furrow; outer surface ornamentation as in LAPs of holotype; four spine


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