Petrocrania, Raymond, 1911
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publication ID |
https://doi.org/ 10.4202/app.2008.0309 |
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persistent identifier |
https://treatment.plazi.org/id/1B17B006-D47A-9731-2D5B-059F42EEF900 |
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treatment provided by |
Felipe |
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scientific name |
Petrocrania |
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Petrocrania View in CoL ? sp.
Fig. 5C.
Material.—One almost complete dorsal valve.
Remarks.—The valve described here is 3 mm wide and 2.8 mm in long, subconical, subtrapezoidal in outline but slightly deformed anteriorly. Posterior margin is short and straight, lateral margins are indented posteriorly and broadly rounded anteriorly. Beak pointed, located less than one−third of valve length from the posterior margin. The surface seems to be partially worn off but ornamentation is evidently limited to weak concentric growth lines only. The interior shows evident punctation but fails to show details sufficient to determine the adductor scars. Absence of spines, radial ornament or lamellose exterior suggest that the specimen may represent Petrocrania but is not specifically definable.
Stratigraphic and geographic range.—This specimen was recovered from sample GB.
Craniidae gen. et sp. indet.
Fig. 6 View Fig .
Material.—Four almost complete and four fragmentary dorsal valves.
Description.—Dorsal valve subpyramidal, with apex displaced posteriorly to centre, and subrectangular in outline; posterior margin nearly straight, long, almost equal the greatest width of the valve which is located near anterior margin. The valve is weakly sulcate from near the apical region and results in a weak median emargination of the anterior margin. Posterior face of the valve slightly concave, forms large subtriangular, steep area ( Fig. 6A View Fig 3). Flanks strongly compressed laterally at one−third of valve length from posterior, resulting in distinct indentation of the lateral margins. Internally, the lateral narrowing forms two symmetric bulges on which a pair of the anterior adductor scars are disposed ( Fig. 6A View Fig 4 View Fig ). Posterior adductor scars not discernible, limbus poorly developed.
External ornament dominated by very strong, thick, slightly irregular costellae which are elevated distally forming finger−like extensions at the periphery of the valve ( Fig. 6A View Fig 4 View Fig , B 1 View Fig , D). Anterolateral costellae are disposed in two bundles which fan out symmetrically on each valve flank ( Fig. A 1 View Fig , C, D 2 View Fig ). Concentric sublamellose ornamentation clearly visible in deep intercostal troughs ( Fig. 6A View Fig 2 View Fig ). Shell substance punctate ( Fig. 6A View Fig 5, A 6 View Fig ).
Remarks.—The exterior of the specimens is bizarre in their unusually strong external ornamentation (at least on some specimens; see Fig. 6A, D View Fig ) and strongly indented lateral margins. These features distinguish the Chinese form from all other craniids known to us. However, the subconical to subpyramidal general aspect, the presence of characteristic muscle scars internally, and punctate shell structure strongly indicates that this is an unknown genus and species of craniid brachiopods. However, insufficient material does not allow for a satisfactory taxonomic diagnosis.
The unusually strong radial costellae arise as rows of fused long extensions formed at valve periphery by radial finger−like appendages of the mantle margin. The costellae are not hollowed but solid and thus strengthened the valve as a probable adaptation to a turbulent environment. Although the specimens studied show a distinct variability in the density of the costellae, they seem to represent one species, as could be ascertained from the same characteristic distribution of the flank costellae, which are grouped in two symmetrical bundles ( Fig. 6A View Fig 1 View Fig , B 2 View Fig , C).
Stratigraphic and geographic range.—This form is known only from sample MH1.
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