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BRITISH DEVONIAN BRACHIOPODA. 



Pealamerus biplicalus occurs in the Middle Devonian limestone of Barton and 

 Lummaton, near Torquay, and has been found by Mr. Chainpernowne in that of Dartington, 

 near Totness. 



Genus Davidsonia, Bouchard, 1849. 

 Davidsonia Vernetjilii, Bouchard. PI. XI, figs. 13, 1G, and PI. XV, fig. 18. 

 Thecidea prisca, Goldfuss, MS. Mus. of Bonn. 



Leptma? Be Verneuil. Geol. of Russia and the Ural, vol. ii, p. 227, pi. xv, fig. 9 ; 

 (mala), 1845. 



Davidsonia Verneuilii, Bouchard. Ann. des Sc. Nat., 3 e . ser., vol. xii, p. 92, pi. i, 



figs. 2 et 2\ 1849. 



— — Be Koninch. Note sur le Genre Davidsonia et stir le Genre 



Hypodema, Annales de la Societe Roy. de Liege, vol. viii, 

 p. 149, pi. i, figs. 1, a — 4, and pi. ii, fig. 1, a, b, 1852. 

 — Bavidson. Introduction, vol. i, p. 110, pi. viii, figs. 186 — 

 193, 1853. 



— — Schnur, in W. Dunker und H. von Meyer's Palseontographica, 



vol. iii, p. 219, pi. xxxix, fig. 4, 1853. 



— Be Koninck. Notice sur une Nouvelle Espece de David- 



sonia; Annales de la Soc. Roy. de Liege, 1855. 



— — Bavidson. Palseontological Notes ; The Geologist, No. XI, 



pi. xii, fig. 33—34, Nov., 1858. 



Spec. Char. Shell transversely oval, with thick unequal valves, fixed to marine objects 

 by a portion of the surface of the back of the ventral valve, filling outward irregularities, 

 but not reproducing them interiorly ; the unattached portion of the ventral valve rises 

 abruptly, especially in front ; hinge-line straight, area more or less denned, and divided 

 by a convex triangular pseudo-deltidium. Dorsal valve slightly convex ; external surface 

 smooth, and marked by concentric lines of growth, which extend uninterruptedly over the 

 rudimentary area. In the interior of the ventral or attached valve, between and below the 

 dental projections, are situated the muscular scars left by the adductor or occlusor muscle, 

 and on either side of these are visible the larger impressions produced by the cardinal or 

 divaricator muscles. In the interior of the dorsal or smaller valve, between the largely 

 developed socket-walls and close to the hinge-line, a small cardinal process is observable, 

 which served for the attachment of the cardinal or divaricator muscles, and under this, on 

 the bottom of the valve, is seen the quadruple impression of the adductor or anterior and 

 posterior occlusors. Proportions variable ; the largest British example yet discovered 

 measured — 



Length 6, width 8 lines. 



05s. Prom the above it has been seen that we have two sets of muscles for the opening 

 and closing of the valves. No trace of adjustor muscles could be ascertained, and these 



