130 BRITISH CARBONIFEROUS BRACHIOPODA 



Orthis resupinata, Martin, sp. PL XXIX, figs. 1 — 6. PI. XXX, figs. 1 — 5. 



Conchyliolithus anomites resupinatus, Martin. Petrif. Derb., tab. xlix, figs. 13, 



14, 1809. 

 Terebratula resupinata, Sow. Min. Con., tab. 325, Feb., 1822. 

 Spirifera resupinata, Phillips. Geol. Yorks., vol. ii, pi. xi, fig. 1, 1836. 



— connivens. lb., fig. 2. 



— resupinata, V. Buck. Mem. Soc. Geol. de France, vol. iv, pi. x, fig. 32, 



1840. 

 Orthis resupinata, De KonincJc. Description des Animaux Fossiles de la Belgique, 



pi. xiii, fig. 9, 1843. 

 Atrypa gibbera, Portlock. Report on the Geology of Londonderry, Tyrone, and 



Fermanagh, pi. xxxviii, fig. 1, 1843. 

 Orthis latisstma, M'Coy. Synopsis of the Carb. Limest. Fossils of Ireland, pi. xx, 



fig. 20, 1844. 

 — ■ gibbera. lb., pi. xviii, fig. 9. 



— resupinata, Dav. 'Introduction,' pi. vii, fig. 135, 1853. 



— — M'Coy. British Palaeozoic Fossils, p. 449, 1855. 



— Dav. Scottish Carb. Bracli., p. 28, pi. i, figs. 1 1, 12, 13, 1860. 



Spec. Char. Shell transversely oval or elliptical ; valves convex, sometimes gibbous ; 

 hinge-line straight, much shorter than the greatest width of the shell, with rounded 

 cardinal angles. Dorsal valve generally the deepest, regularly and evenly convex, or 

 slightly flattened and depressed along the middle to the front, area narrow. Ventral 

 valve variable in its curves, moderately convex throughout, or at the rostral portion only, 

 becoming flattened or slightly concave near the lateral and frontal margins. The frontal 

 margin presents a uniform or undulated curve, indenting to a lesser or greater extent the 

 margin of the opposite valve. Beak small and moderately incurved ; area triangular, with 

 an open fissure. Exteriorly, the valves are closely covered with numerous fine, thread-like, 

 rounded, radiating striaj, which increase in number by interstriation and bifurcation at 

 variable distances from the beaks, and at intervals the striae themselves augment in 

 thickness and prominence, producing small, hollow, thread-like, tubular spines, which 

 become more numerous towards the margin. The intimate shell structure is perforated 

 by innumerable canals, of which the exterior orifices, in the shape of minute punctures, 

 cover the entire surface of the valves. 



In the interior of the ventral valve, the dental plates extend to some distance along the 

 bottom of the shell, and between these a small rounded or angular ridge divides the 

 muscular scars, which thus form two elongated depressions margined on their outer sides 

 by the prolonged basis of the dental plates. The adductor or occlusor leaves a small, 

 not always clearly defined impression on either side of the mesial ridge, and it is probable 



