Lamellispina, Sun & Baliński, 2008

Sun, Yuanlin & Baliński, Andrzej, 2008, Silicified Mississippian brachiopods from Muhua, southern China: Lingulids, craniids, strophomenids, productids, orthotetids, and orthids, Acta Palaeontologica Polonica 53 (3), pp. 485-524 : 515-516

Genus Lamellispina nov.

Type species: Lamellispina spinosa gen. et sp. nov., by monotypy.

Etymology: From the characteristic ornamentation of the shell of concentric lamellae and radial spinous projections.

Diagnosis.—Small to medium sized orthotetoid cemented (at least at the earlier ontogenetic stages) at its asymmetrical ventral umbo; ventral valve subconical with high interarea and strongly convex pseudodeltidium, without perideltidium or monticulus; dorsal interarea low, but wide to linear, chilidium convex with median groove. Dental ridges unsupported by dental plates, not developed umbonally; median septum absent; cardinal process low, bilobed; socket ridges divergent, partially ankylosed to cardinal process. Ornamentation lamellose and strongly costellate by intercalation; costellae extend at periphery of concentric lamellae as spinous projections inclined at low angle away from the valve surface. The genus differs from the majority of schuchertellids in its lamellose−costellate ornamentation with a tendency to produce spinous projections. From Goniarina Cooper and Grant, 1969 , Bothrostegium Cooper and Grant, 1974 , and Chelonomia Cooper and Grant, 1974 it differs by less conical ventral valve. From Streptorhynchus King, 1850 it differs mainly in the absence of monticulus and having low cardinal process.

Remarks.—The most important shell features defining the new genus are: the subconical ventral valve, asymmetrical ventral umbo with a cicatrix, absence of a perideltidium, monticulus, and dental plates, and divergent socket plates ankylosed to the bilobed cardinal process. These characteristics strongly suggest that Lamellispina belongs to the family Schuchertellidae Williams, 1953 . Subfamily affiliation is more difficult, but the presence of low cardinal process lobes and absence of a perideltidium and monticulus in Lamellispina gen. nov. precludes its attribution to Streptorhynchinae Stehli, 1954 and is more in agreement with characteristics of the Schuchertellinae Williams, 1953 .

One of the most characteristic features of the genus, however, is its shell ornamentation combining concentric lamellose structure and strong radial costellae which form long, half−tube projections at the periphery of concentric lamellae. The combination of the above features helps to discriminate this newly proposed genus from all known orthotetoids, and, particularly, schuchertellids. By having distinct lamellose−costellate ornamentation Lamellispina resembles Goniarina , Bothrostegium , Chelononia , and Streptorhynchus . The first three genera, however, are much younger stratigraphically, coming from the Early Permian of Texas ( Cooper and Grant 1969, 1974) and they all have more conical ventral valve. The new genus differs from Goniarina also by having divergent, not recurved, socket ridges. From Bothrostegium it is distinguished also by the absence of a perideltidium and shorter cardinal process lobes, and from Chelononia it differs by having wider hinge margin, shorter cardinal process, and lacking a monticulus. The last two features separate the new genus also from the Carboniferous–Permian genus Streptorhynchus .

Although the presence of distinct spine−like, half−tube outgrowths in Lamellispina is a very important distinguishing feature, we do not overemphasize it when comparing the new genus with other orthotetoids because the recognition of such delicate structures may depend importantly on taphonomic characteristics of the material.

Stratigraphic and geographic range.—The genus is known only from its type locality and type horizon.