MONELASMINIINAE Harper, 2000

Mottequin, Bernard, 2008, New observations on Upper Devonian brachiopods from the Namur-Dinant Basin (Belgium), Geodiversitas 30 (3), pp. 455-537 : 474-478

Subfamily MONELASMINIINAE Harper, 2000

FIG. 17. —? Hypsomyonia sp. , complete shell (IRScNB a12358), Genus Monelasmina Cooper, 1955 loc.BM-2002-5, Les Valisettes Formation: A, ventral view; B, dorsal view; C, lateral view; D, posterior view; E, anterior view. Scale TYPE SPECIES. — Orthis deshayesi Rigaux, 1873 , by bar: 1 mm. original designation.

45, pl. 2, fig. 1) from the Famennian of the Aachen Monelasmina cf. deshayesi (Rigaux, 1873) area belong probably to A. aggeris n. sp. (Figs 18; 19; Table 2)

Family HYPSOMYONIIDAE Wright, 1965

Orthis deshayesii Rigaux, 1873: 50 , pl. 1, fig. 4.

? Skenidium Lemeslii – Maillieux 1909a: 12.

Genus Hypsomyonia Cooper, 1955 Mystrophora deshayesi – Maillieux 1941b (e.p.): 3.

Monelasmina deshayesi – Brice 1981: 142.

TYPE SPECIES. — Hypsomyonia stainbrooki Cooper, 1955 , by monotypy. MATERIAL EXAMINED. — BM-2003-3 (13 articulated specimens, eight ventral valves); BM-2003-4b (nine articulated specimens,six ventral valves, two dorsal valves); BM-2003-6

? Hypsomyonia sp. (11 articulated specimens, one ventral valve).

(Fig. 17; Table 2)

DESCRIPTION

MATERIAL EXAMINED. — BM-2002-5 (one articulated Shell small-sized, wider than long (width/length specimen). ratio: 1.03-1.29), ventribiconvex, semi-elliptic in outline; hinge line shorter than greatest width (hinge

REMARKS line width/width ratio: 0.61-0.77); widest at about This identification is made for a very small shell with mid-length; anterior margin straight to rounded; a roughly elliptical outline displaying the following anterior commissure unisulcate. external characters: unisulcate anterior commissure; Ventral valve regularly and moderately curved in short hinge line; widest at about mid-length; ven- lateral profile; flanks sloping moderately towards tral valve devoid of fold and sulcus; ventral inter- lateral commissure; beak curved on the interarea; area low, slightly apsacline, weakly concave; dorsal shoulder lines concave to broken; shoulder and sulcus well-defined, originating close to the apex, apical angles between 125-141° and 107-128°, ornamentation costellate; costellae increasing by respectively; interarea well-developed, of variable intercalation; 6 or 7 costae and costellae per 1 mm concavity, cata-apsacline; delthyrium open.

Upper Devonian brachiopods from Belgium

Dorsal valve roughly oval in outline; posterolateral areas inclined to become flat; wide and shallow median depression, originating at about mid-length; tongue rounded, not perpendicular to the commissural plane; interarea anacline, flat, less developed than the ventral one; notothyrium open.

Ornamentation multicostellate; 20-23 costae and costellae per 5 mm at the anterior margin; costellae increasing by intercalation; growth lamellae rare,

thickened close to the commissure.

Internal characters not studied.

DISCUSSION The specimens of Monelasmina which have been collected in Frasnes and Cerfontaine are compared Fshell IG. 18 (IRScNB. — Monelasmina a12361),loc cf.BM-. deshayesi 2003 -6 (, Rigaux Grands, Breux 1873), Formation complete to M. deshayesi . As is the case in M. deshayesi , these (Boussu-en-Fagne Member): A, ventral view; B, dorsal view; C, lateral small shells display a median dorsal depression of view; D, posterior view; E, anterior view. Scale bar: 5 mm. variable depth, as well as an unisulcate anterior commissure. However, the specimens from Frasnes and 94-118°, respectively; interarea well-developed, are always wider than long, with sometimes a wider apsacline, concave; delthyrium open. hinge line, thus an outline somewhat different from Dorsal valve regularly convex in lateral profile; the one of M. deshayesi . median depression occurring exceptionally; tongue absent or hardly developed; interarea anacline, flat DISTRIBUTION to slightly concave, about two times less high than Monelasmina cf. deshayesi occurs in the Grands Breux the ventral one; notothyrium open. Formation (Boussu-en-Fagne Member; southern bor- Ornamentation multicostellate; costellae appear- der of the Dinant Synclinorium) as well as in the Les ing by intercalation or more rarely by bifurcation; Valisettes Formation (Philippeville Anticlinorium). (19?) 20-25 costae and costellae per 5 mm at the anterior margin; growth lamellae thickened close to the commissure.

Monelasmina sp. A Ventral interior with short dental plates supporting

( Figs 19 -21) teeth rectangular in transverse section; lateral apical cavities small; muscular field not observed. MATERIAL EXAMINED. — BM-2002-5 (26 articulated Dorsal interior with deep notothyrial cavity with specimens, 43 ventral valves, 17 dorsal valves).

bilobed cardinal process; internal crests of dental sockets well-developed; brachiophores thickened, DESCRIPTION pointed anteriorly; median septum very long, touch- Shell small-sized, more or less equidimensional to ing the floor of the opposite valve; muscular field wider than long (width/length ratio: 1.02-1.39), limited by low ridges. ventribiconvex, subcircular in outline; hinge line shorter than greatest width (hinge line width/width DISCUSSION ratio: 0.66-0.89); widest at about mid-length; This species has been previously identified as Moneanterior commissure rectimarginate to vaguely lasmina deshayesi (Rigaux, 1873) from which it unisulcate. differs by its larger size, its rectimarginate anterior Ventral valve regularly convex; beak hardly curved commissure, its more developed ventral interarea and on interarea; umbo prominent; shoulder lines bro- its wider hinge line. Monelasmina sp. A differs from ken; shoulder and apical angles between 129-152° M. cf. deshayesi by its larger size, a more developed

Mottequin B.

Monelasmina sp. A N = 25

W = 6.99 mm L = 6.15 mm T = 3.84 mm

10 10 Monelasmina deshayesi N = 50

W = 5.53 mm 0 L = 5.28 mm 0 T = 2.72 mm 0.85 0.95 1.05 1.15 1.25 1.35 0.35 0.45 0.55 0.65 0.90 1.00 1.10 1.20 1.30 1.40 0.40 0.50 0.60 W/L T/W

ventral interarea, a rectimarginate or indistinctly thus, a less rounded outline. Monelasmina sp. A unisulcate anterior commissure. Monelasmina sp. is close to M. wenjukovi Liashenko, 1959 , but its A is distinguished from M. besti Pedder, 1959 by anterior commissure is generally rectimarginate and the absence of ventral fold, its wider hinge line and, its ventral beak is less curved on the interarea.

Upper Devonian brachiopods from Belgium 2.25

2.95 5.35 7.05

DISTRIBUTION Schizophoria gr. striatula Monelasmina sp. A occurs within the Les Valisettes (von Schlotheim, 1813) Formation on the southeastern border of the Dinant ( Fig. 22 ) Synclinorium, but it could be present also in the Neuville Formation in this area.

Anomites Terebratulites striatulus von Schlotheim, 1813:

pl. 1, fig. 6, non p. 76 (see Biernat [1959], Pocock

[1966] and Struve [1964] for a complete synonymy

Family SCHIZOPHORIIDAE outside Belgium).

Schuchert & LeVene, 1929

Genus Schizophoria King, 1850 REMARKS

The revision of Schizophoria species in the Frasnian TYPE SPECIES. — Conchyoliolithus ( Anomites ) resupinatus formations sampled has not been carried out. They Martin, 1809, by original designation. are assigned to the group of S. striatula , a species

Mottequin B.

would be only Frasnian in age, but he has only figured its lectotype. Pocock (1966: 386, 402) recognized two species in the Frasnian of the Namur-Dinant Basin: S. (Paraschizophoria) antiqua Solle, 1936 and S. striatula on the basis of the old collections of the IRScNB but a modern study is urgently needed.

Figures

FIG. 19. — Comparison between Monelasmina sp. A (loc. BM-2002-5, Les Valisettes Formation) and Monelasmina deshayesi (Rigaux, 1873) (according to Brice’s (1981) measurements of specimens from Boulonnais). Scatter diagrams of shell width (W) to shell length (L), shell width to shell thickness (T); frequency diagrams of W/L and T/W. Dotted lines indicate the means.

FIG. 22. — Schizophoria gr. striatula (von Schlotheim, 1813): A-E, complete shell (IRScNB a12365), loc. BM-2003-7, Grands Breux Formation (Boussu-en-Fagne Member); F-J, complete shell (IRScNB a12366), loc. Durbuy 5337, Barvaux Formation; A, F, ventral views; B, G, dorsal views; C, H, lateral views; D, I, posterior views; E, J, anterior views. Scale bars: 10 mm.