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Journal of Paleontology 91(4):715–734 Although the posterior plating of Ambonacrinus is similar
to that of Cefnocrinus and Pararchaeocrinus, it is most morphologically similar to Rhaphanocrinus Wachsmuth and Springer, 1885 on the basis of its strong median ray ridges, hidden infrabasals, fixed secundibrachials and intersecundibra- chials, anal series in the posterior interray, and ten uniserial arms. Ambonacrinus is differentiated from Rhaphanocrinus by its subconical calyx, contact of the primanal with the C-ray primibrachial, and origin of the anal series and anitaxial ridge from the C-ray primibrachial. By contrast, Rhaphanocrinus has a calyx shape that ranges from bowl shaped to globose, primanal located above the CD basal, and anal series that originates from the center of the interray.
Ambonacrinus decorus new species Figures 3.3–3.6, 4.4, 4.5
Holotype.—The holotype, MPZ2016/94, is the only known specimen of this species.
Diagnosis.—Rhodocrinitid with medium conical calyx; infra- basals hidden; median ray ridges; all interrays in contact with tegmen; CD interray wider, anal series with anitaxial ridge originating from C-ray primibrachial; fixed primibrachials and secundibrachials; intrabrachial plates between fixed secundi- brachials; 10 free arms, branched isotomously; brachials recti- linear uniserial.
Occurrence.—Fombuena Formation, Huerva Member, upper middle Berounian (lower Katian, Upper Ordovician), near Fombuena (Zaragoza province), Spain; Locality 2.
Description.—Calyx medium conical, wider than high; plates
with heavy stellate ornamentation; plate sutures indistinct, flush with plate surface; ray ridges prominent, bulbous, ornamented with irregular parallel ridges, widest at plate sutures; calyx base surrounded by stellate rim. Infrabasal plates likely five, completely hidden by stem.
Basal circlet forming rim of basal concavity, visible in side view, proximal margin covered by stem; basal plates five, largest plates in calyx, hexagonal, truncated distally, as high as wide.
Radial circlet interrupted in all rays; radial plates five,
primanal. First well-defined anal plate in contact with C-ray first primibrachial and upper left margin of C radial; anal series originating from C-ray first primibrachial, comprised of a column of hexagonal plates with prominent anitaxial ridge. Proximal plating 1-3-3-3?, higher ranges of plates unknown. First primibrachial fixed, hexagonal, wider than high;
pentagonal, wider than high. Regular interrays in contact with tegmen, slightly depressed, interrupting the radial circlet in all rays. First interradial plate septagonal, as wide as high. Higher ranges of plates undefined. Posterior interray wider, in contact with tegmen. First plate in the center of CD interray not clearly differentiated as
second primibrachial axillary, pentagonal. Secundibrachials free above second or third secundibrachial. Intrabrachial plates between each adjacent half ray; plating pattern unknown.
Etymology.—Decorus, after the Latin for ornamented or deco- rated, in reference to the elegant ornamentation of the calyx.
Measurements.—Holotype measurements are given in Table 2. Diplobathrida genus indeterminate species indeterminate Figure 6.1
Remarks.—This species is represented by one specimen that consists of a crushed partial calyx and proximal stem. The spe- cimen preserves incomplete proximal circlets, an interior por- tion of the theca, and some surrounding disarticulated plates. Infrabasal plates are as wide as high with an imprint of the circular stem cicatrix. Basal plates are hexagonal, wider than high, ornamented with stellate ridges, and proximally flared to form the rim of a basal concavity. The stem is circular and heteromorphic with noditaxis sequence N3231323. The presence of an infrabasal circlet and interradial plates
indicates this specimen belongs to Diplobathrida. Ornamenta- tion of the calyx plates and arrangement of stem nodals and internodals are similar to those of Goyacrinus gutierrezi, and this specimen may belong to that species. Because other circlets and interrays are indistinguishable, however, it is not possible to confidently identify this specimen beyond the level of order.
Figure 6. Unidentified camerates from the Fombuena Formation of Spain. (1) Diplobathrida gen. indet. sp. indet., internal view of disarticulated calyx and proximal stem, MPZ2016/104; (2) Camerata gen. indet. sp. indet., basal view of partial calyx and proximal stem, MPZ2016/93.
Arm openings 10, ungrouped; free arms branching once
isotomously. Brachials rectilinear uniserial proximally, weakly cuneate uniserial distally. Pinnules on every free brachial; D ray pinnule enlarged on side of CD interray ray. Tegmen and anal opening unknown. Proximal stem circular, heteromorphic, holomeric. Lumen, internoditaxis sequence, distal stem, and holdfast unknown.
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