Syncyclonema hagenowi Dhondt, 1971
DHONDT, A. V. 1971. Systematic revision of Entolium, Propeamussium (Amusiidae) and Syncyclonema (Pectinidae, Bivalvia, Mollusca) of the European Boreal Cretaceous. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, 47 (32): 1-95, pls. 1-4 [p. 68, pl. 3, figs. 1a-1c]
1971 Syncyclonema hagenowi Dhondt, 1971
A. V. Dohndt, 1971, plate 3.
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Derivatio nominis:
In honour of F. VON HAGENOW who described the Maastrichtian fauna of the Island Rügen (German Democratic Republic). Nomenclature:
The name Pecten hagenowi has been found on manuscript labels by NYST & DE KONINCK in the collections of the I. R. Sc. N. B. Holotype and Paratypes:
I. R. Sc. N. B., type-collection 9853: holotype; 9854 & 9855: paratypes. Stratum typicum:
Upper Maastrichtian (Craie tuffacée). Locus typicus:
Saint-Symphorien, Hainaut, Belgium. Description of holotype and topotypes
Number of studied specimens: 99 from the type-area. Measurements:
umbo~palleal diameter: from 31 mm to 71 mm; av. 51.5 mm (n = 87) width: from 32 mm to 68 mm av. 48.0; (n = 87) A. A. : from 90° to 119°; av. 100°; (n = 87) index U.P. D. / W from 0.9038 to 1.2400; av. 1.0721. Description:
Diagnosis. — Medium to large Syncyclonema-species with pronounced concentric ornamentation on both valves, with straight apical and hinge margins. macrosculpture: both valves are covered with well developed concentric ridges; on poorly preserved valves these are not clearly visible. Their number varies between 15 and 27. Near the pallial margin they are closer to one another than in the umbonal area. right valve: anterior auricle has an equilateral triangular shape and a deep byssal sinus which reaches about half the lenght of the auricle. posterior auricle: almost right angled and half the size of the anterior auricle. The concentric ridges are continued on the anterior auricle as lines and lie closer to each other than on the disc. left-valve: both auricles are right-angled but the anterior is about twice the size of the posterior. Hinge margin and apical margins are straight; the latter reach about half the lenght of the U. P. D. Discussion
Among the European Syncyclonema-species this is the only one with a concentric macroscopical ornamentation on both valves.
On many specimens the radial diverging Camptonectes-vermiculations are macroscopically visible (pI. Ill, f. 3 b). S. hagenowi can be differentiated — from S. halli (GABB) by its larger size. smaller auricles, more pronounced concentric ornamentation on both valves, and by its more orbicular shape. — from S. nilsoni (GOLDFUSS) by its higher shape, generally smaller size, longer and straight apical margins, almost straight hinge-margin, and concentric macrosculpture. — from S. haggi nom. nov. by its larger size, smaller auricles. shorter apical margins, concentric ornamentation. The auricles have a different surface distribution in both species: S. hagenowi: P/A = 1/2; S. haggi: P/A = 1/3 — from S. gamsensis nom. nov. by its larger size, less convex shape, and concentric macrosculpture. — from S. haldonensis by its smaller auricles. Generic attribution:
The unequal auricles, well developed byssal sinus and concentric macrosculpture explain the attribution to Syncyclonema. Stratigraphical and geographical distribution
Maastrichtian: BELGIUM:
Cuesmes, Saint-Symphorien and Spiennes: «Craie phosphatée» Ciply. Ciply-Malogne: «Poudingue de la Malogne A» Ciply, Mesvin-Bélian, Saint-Symphorien: «Craie Tuffeau de Saint-Symphorien » (all specimens in I. R. Sc. N. B.)» ANNIE VALÉRIE DHONDT, 1971
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