790
Journal of Paleontology 91(4):781–798
shorter, equally poorly defined spur ventrally; proximal edge paralleled by a conspicuous, deep furrow; distal half of ventral edge in proximal and median LAPs weakly concave; distal LAPs with evenly convex ventral edge. Outer surface stereom of LAPs moderately finely meshed and with weakly enlarged, vertically elongate, and densely packed trabecular intersections; faint horizontal striation lining the distal edge of the furrow paralleling the proximal LAP edge. Three to four relatively large spine articulations sunken in shallow depressions of the distal portion of the LAP at some distance from the distal edge and tightly encompassed by the outer surface stereom; strong dorsalward increase in the size of the spine articulations and the distance separating them; spine articulations composed of a large, round muscle opening proximally tightly encompassed by a relatively low, semicircular, irregularly denticulate ridge and distally separated from a slightly smaller nerve opening by a thicker, more prominent but shorter vertical oblique ridge composed of slightly more densely meshed stereom. Inner side of LAPs with large ventral and dorsal contact
surfaces with opposite LAP; short, wide, well-defined, and prominent central ridge on elevated part connecting the ventral and dorsal contact surfaces with the opposite LAP, widest ventrally and with a tongue-shaped, slightly proximalward- pointing dorsal tip; inner side of distal edge lined with poorly defined, very weakly prominent vertical surface composed of more densely meshed stereom; large, deep, sharply defined ventralward- (proximal LAPs) to ventro-distalward-pointing (median LAPs) tentacle notch; distal LAPs with large ventro- distalward-pointing tentacle perforation. No further perforations discernible on inner side.
Remarks.—The neotype and associated specimens were duly described and illustrated by Hess (1964). There is nothing to add from our observations of the type material. To facilitate comparison with other species, in particular those known exclusively from dissociated LAPs, we redescribe and illustrate the LAPs from the Callovian of Switzerland originally described by Hess (1963) as Ophiomusium calloviense and shortly after synonymized with Ophioderma (now Enakomusium) weymouthiense (Hess, 1964) using the terminology by Thuy and Stöhr (2011). The LAPs of Enakomusium weymouthiense bear strong
similaritieswith those described by Thuy (2015) as Enakomusium leckenbyi (Wright, 1880) and Enakomusium ferrugineum (Boehm, 1889), corroborating their assignment to the same genus (Thuy and Stöhr, 2011). The main difference put forward by Thuy (2015)was the grouped ventral spine articulations separated from the dorsal-most one by a gap. Our redescription suggests a strong but continuous dorsalward increase in the distance separating the spine articulations, rather than a ventral grouping and a dorsal
gap.Another noteworthy differencewith the LAPs of E. leckenbyi and E. ferrugineum is that the spine articulations of E. weymouthiense are sunken in shallow depressions. Differences with the new species Enakomusium whymanae are discussed in the preceding.
Occurrence.—Radipole Backwater or Ham Cliff, Weymouth, Dorset; Weymouth Member, early Oxfordian, Late Jurassic.
Genus Aspidophiura Matsumoto, 1915
Type species.—Aspidophiura watasei Matsumoto, 1915, by original designation
Aspidophiura? seren new species Figure 5.4–5.7
Holotype.—NHMUK EE 16212.
Diagnosis.—Species with relatively large, nearly rectangular LAPs, wider than high, with slightly concave dorsal edge, finely meshed outer surface stereom with small trabecular intersec- tions; smooth proximal edge; three to four spine articulations integrated in the distal edge of the LAPs; single, large central ridge on inner side; proximal LAPs with deep tentacle notch distally encompassed by a strongly protruding ventrodistal tip of the LAP; median and distal LAPs with a large tentacle perforation.
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 16212 (Fig. 5.4) is a dissociated proximal LAP of rectangular outline, slightly wider than high, with weakly concave dorsal edge, convex distal edge, and irregularly convex ventral edge; ventrodistal tip of LAP strongly protruding; proximal edge of LAP concave, smooth, devoid of discernible spurs, and with a narrow band of more finely meshed stereom; outer surface of LAP with finely meshed stereom with small trabecular intersections, no vertical or horizontal striations discernible. Three spine articulations sunken in distal edge of LAP, tightly encompassed by outer surface stereom, nearly of equal size; gap between the ventral andmedian spine articulations slightly larger than between the dorsal and the median ones; spine articulations composed of an irregularly shaped muscle opening proximally bordered by a thin, poorly defined, and weakly prominent vertical ridge and distally separated from the slightly smaller, round nerve opening by a large, prominent, well-defined, and straight vertical ridge. Inner side of LAP with a single, large, well-defined oblique
ridge, widest at rounded dorsal tip; ventral tip of ridge merged with ventral portion of LAP; dorsal and ventral contact surfaces with opposite LAP thin; inner side of distal edge smooth, with a poorly defined band of more finely meshed stereom; deep, sharply defined, ventralward-pointing tentacle notch almost completely encompassed by the slightly thickened ventrodistal edge of the LAP; no perforations discernible.
Paratype supplements.—EE 16213 (Fig. 5.6) is a dissociated proximal LAP, slightly wider than high, with a straight dorsal tip and strongly ventroproximalward-protruding ventral portion; proximal edge and outer surface as in holotype; spine articulation morphology as in holotype except for a larger gap between the dorsal and median spine articulations; tentacle notch deep but not as closely encompassed as in holotype; ridge on inner side of LAP narrower than in holotype.
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