Georgethyris Minato, 1953
|
publication ID |
https://doi.org/ 10.4202/app.00972.2022 |
|
persistent identifier |
https://treatment.plazi.org/id/41708783-FFFD-FF91-8C8B-CBFCFD8EFD82 |
|
treatment provided by |
Felipe |
|
scientific name |
Georgethyris Minato, 1953 |
| status |
|
Genus Georgethyris Minato, 1953
Type species: Reticularia alexandri George, 1932 , from the Brigantian , uppermost Visean , of Settle, Yorkshire, England .
Georgethyris lobata ( Muir-Wood, 1926)
Fig. 16H View Fig .
1926 Reticularia lobata ; Muir-Wood 1926: 242, pl. 16: 1a–c, 2.
1932 Reticularia lobata Muir-Wood, 1926 ; George 1932: 560.
1991 Georgethyris lobata ( Muir-Wood, 1926) ; Brunton and Tilsley 1991: 293.
Material.— One articulated specimen: MPUM12086 View Materials (WI1- 9) from Wensley Dale , Matlock , Derbyshire, UK, Eyam Limestone Formation , upper Brigantian, upper Visean .
Description.—Small, ventribiconvex shell with transversely sub-exagonal outline; cardinal margin straight, corresponding to half shell width; maximum width at shell mid-length. Anterior commissure paraplicate. Ventral umbo enrolled; interarea apsacline. Subangular sulcus starting 7.0 mm from the umbo, widening and deepening anteriorly, prolonged anteriorly as a subangular tongue; two rounded, low folds bordering the sulcus. Dorsal interarea apsacline, very low. Rounded dorsal fold starting 7.0 mm from the beak. Both valves covered by subimbricated lamellae, numbering 12 per 5.0 mm length. Dorsal adminicula and septum absent.
Remarks.—The specimen is assigned to Georgethyris lobata based on its paraplicate commissure, which distinguishes it from G. alexandri and G. obtusa , and the lower, broader fold with respect to G. acutiloba ( George 1932: pl. 34: 2a–d). Moreover, G. acutiloba shows a more transverse outline. The specimen is smaller than the specimens of G. lobata recorded by Muir-Wood (1926) and George (1932).
Stratigraphic and geographic range.— Georgethyris lobata is recorded in the Chadian–Brigantian (Visean) of England (e.g., Mitchell 1971; Brunton and Tilsley 1991; this study).
Family Elythidae Fredericks, 1924
Subfamily Phricodothyridinae Carter, 1939
Genus Phricodothyris George, 1932
Type species: Phricodothyris lucerna George, 1932 , from the Visean of Lowick , Northumberland, England .
Remarks.—The genus was erected by George (1932) and emended by Minato (1953) to include lamellose spiriferides with biramous spines showing no ventral adminicula nor median septa, whose absence allows to distinguish it from all other Mississippian Elythidae . Moreover, Phricodothyris differs from Nebenothyris Minato, 1953 , from the Mississippian of Western Europe and Japan, in having a fainter, but denser concentric ornamentation.
Carter and Gourvennec (2006) described Phricodothyris as having no fold-sulcus: however, this is not always true, as Phricodothyris periculosa George, 1932 , shows a shallow ventral sulcus.
Phricodothyris paricosta George, 1932
Fig. 16I–K View Fig .
1932 Phricodothyris paricosta ; George 1932: 548, pl. 35: 4a–d.
Material.—Three ventral valves: MPUM 12054 ( RCC 40- 10a); MPUM 12055 ( RCK 15-34b); MPUM 12056 ( RCC 54- 6). Three dorsal valves: MPUM 12057 ( RCK 15-9); MPUM 12058 ( RCK 15-34a); MPUM 12059 ( RCC 2-6a). All from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian, upper Visean.
Description.—Small, ventribiconvex shell with transversely suboval outline. Cardinal margin straight; maximum width attained at shell mid-length. Anterior commissure rectimarginate. Ventral umbo straight to gently curved, interarea low, apsacline.
Ornamentation consists of regularly spaced (1.2–1.6 mm) subimbricated lamellae, each one bearing a single row of prominent, elongated spine bases. Spine bases on adjacent lamellae are aligned so that a ribbing-like pattern is developed. Spine bases number 6–8 per 5.0 mm width, 10.0 mm from umbo.
Ventral adminicula absent.
Remarks.—The specimens are included in Phricodothyris paricosta , from the Brigantian (uppermost Visean) of Northumberland, based on their rectimarginate commissure and ornamentation of widely spaced lamellae bearing coarse spine bases.
Stratigraphic and geographic range.— Phricodothyris paricosta is recorded in the Visean of Great Britain and Ireland ( George 1932; Mitchell 1971).
Phricodothyris cf. periculosa George, 1932
Fig. 16L–N View Fig .
Material.—Six articulated specimens: MPUM 12060 ( RCC 73-30a); MPUM 12061 ( RCK 15-3); MPUM 12062 ( RCC 60- 10, 56); MPUM 12063 (WI1-8, 18). Four ventral valves: MPUM 12064 ( RCC 2-37); MPUM 12067 ( RCC 1-53a, 53b; RCC 54-14). One fragment: MPUM 12068 ( RCC 38A-1). All from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian (RCC-, RCK-), and Wensley Dale, Matlock, Derbyshire, UK, Eyam Limestone Formation, upper Brigantian, upper Visean (WI1).
Description.—Small, ventribiconvex to equally biconvex shell with suboval outline; cardinal margin straight; maximum width attained at shell mid-length. Anterior commissure rectimarginate to slightly uniplicate. Ventral interarea low, apsacline. Shallow sulcus develops at 10.0 mm from the umbo. Entire surface of both valves covered by lamellae, 10–12 per 5.0 mm length. Adminicula and median septa absent. Spiralia laterally directed.
Remarks.—The specimens are compared to Phricodothyris periculosa George, 1932 , from the upper Visean–lower Serpukhovian of Yorkshire, England, which is characterised by shallow sulcus and an ornamentation of closely spaced lamellae bearing numerous fine spine bases. The specimens differ from P. paricosta from the same localities by the presence of a ventral sulcus developed from shell mid-length and by their denser lamellose ornamentation.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
|
Kingdom |
|
|
Phylum |
|
|
Family |
Georgethyris Minato, 1953
| Carniti, Alessandro P., Porta, Giovanna Della, Banks, Vanessa J., Stephenson, Michael H. & Angiolini, Lucia 2022 |
Georgethyris lobata ( Muir-Wood, 1926 )
| Brunton, C. H. C. & Tilsley J. W. 1991: 293 |
Reticularia lobata
| George, T. N. G. 1932: 560 |
Phricodothyris paricosta
| George, T. N. G. 1932: 548 |
Reticularia lobata
| Muir-Wood, H. M. 1926: 242 |