BRITISH TERTIARY BRACHIOPODA. 



species of Lingula, as these generally vary but little from one another. Sir C. Lyell 

 remarks, in his ' Elementary Geology,' that the presence of species of Lingula in the Crag 

 is worthy of notice, as these Brachiopoda seem now confined to more equatorial seas. 



Plate I: figs. 10 and 11, are figured from specimens found in the Crag of Sutton, and 

 kindly lent to me by Mr. S. Wood. 



Fig. 10*. Interior of the smaller valve considerably magnified. 



Fig. 10 *. Interior of the larger valve likewise magnified. 



2. Lingula tenuis, Sow. Plate I, fig. 12. 



Lingula tenuis, Sow. M. C, tab. xix, fig. 3, p. 55, vol. i, 1812. 



— — Morris. Catalogue, 1843. 



— — Tennant. A Stratigraphical List of Br. Fossils, p. 32, 1847. 



— — Bronn. Index Pal., vol. i, p. 656, 1849. 



Diagnosis. Shell of a lengthened, lanceolate, oval form, flattish, the anterior edge 

 short and straight ; surface smooth, bright and shining, marked by numerous concentric 

 lines of growth. Length 5 ; width 1^ lines. 



Obs. This small species is described by Sowerby as not unfrequent in the sandy 

 limestone of Bognor. It has also, I believe, been found near Highgate, in the London 

 Clay ; it is easily distinguished from Lingula Dumontieri, Nyst, {L. fusca, S. Wood,) by 

 its dimensions and more lanceolate shape. 



Plate I, fig. 12, from the original specimens in the Min. Con. ; we regret having been 

 unable to procure better specimens for illustration. 



Genus — Orbicula, Cuvier. 1808. 



Shell inequivalved, more or less orbicular, upper valve conical, with apex inclining 

 towards the posterior margin, lower valve depressed, pierced by a longitudinal fissure, from 

 which issues a tendinous pedicle spreading over a small disk placed near the posterior part 

 of the lower valve, and externally adhering to rocks, corals, and other substances; valves 

 smooth, concentrically lamellose or longitudinally striated; structure almost entirely horny; 

 animal symmetrical, mantle free all round, with numerous long, horny and unequal cilia, 

 body small; no calcareous supports; arms fleshy, ciliated, and united at their origin above 

 the mouth, free only at their short spiral portion ; muscular system composed of eight 

 distinct muscles, leaving two oval impressions in upper or unattached valve, near the 

 posterior margin, and two others near the palleal region. 1 



Obs. We are not acquainted with any British recent orbicula, one only is found in the 

 supercretaceous deposits. 



1 For more ample details, consult Professor Owen's excellent description of the animal of this genus, 

 'Zool. Trans.,' vol. i, 2d part. 



