20 BRITISH CRETACEOUS BRACHIOPODA. 



Tekebratula pumila, Von Buch. Uber Ter., 1834; and Mem. de la Soc. Geol. de 

 France, vol. iii, 1st ser., p. 206, pi. xix, fig. 5, 1838. 

 — concava, Deshayes. 183G. Nouv. Ed. de Lamarck, vol. vii, No. 26. 



Magas pumilus, Bronn. Leth. Geog., p. 662, pi. xxx, fig. 1, 1837. 



— — Brown. Illustr. of Fossil. Conch., pi. xlix, figs. 5 and 13, 1838. 



— — Morris. Catalogue, 1843. 



— — D'Orb. 1845. Geol. of Russia and Oural, vol. ii, p. 495, pi. xliii, 



figs. 27—30. 

 — D'Orb. 1847. Pal. Franc. Ter. Cr^taces, vol. iv, p. 54, pi. 501. 



— — Bouchard and Dav. Bulletin de la Soc. Geol. de France, vol. v, 



2d ser., p. 139, pi. ii, figs. 1—11, 1848; and Dav., Bull. Soc. 

 Geol. Fr., vol. vii, 2d ser., p. 62, pi. i, figs. 7—9, 1849. 



— — Bronn. Index Pal., p. 699, 1848. 



— — Tennant. Strat. List of Brit. Fos., p. 47, 1847. 



— — Dav. Annals and Mag. of Nat. Hist., vol. v, pi. xv, fig. 2, 1850. 



— — D'Orb. Prodrome, vol. ii, p. 258, 1850. 



Diagnosis. Shell equilateral, inequivalve, oval or circular ; larger valve convex ; beak 

 more or less recurved, sometimes almost straight, slightly truncated by a triangular 

 foramen extending from the beak to the umbo ; deltideum small and lateral, not sur- 

 rounding the foramen ; false area small or large ; imperforated valve slightly concave or 

 moderately convex ; surface smooth, marked by numerous concentric lines of growth ; 

 structure largely or more or less closely punctuated in the form of lozenge-shaped punc- 

 tures. The apophysary system is complicated, composed, in the smaller valve, of a mesial, 

 longitudinal, elevated triangular septum, extending to about two thirds of the length of 

 the valve, arising from under the crura by a gentle curve, reaches and touches the 

 larger valve near its centre, whence it descends by an almost perpendicular line to the 

 bottom of the valve; to this septum are attached two pairs of calcareous lamella?, 

 differently shaped ; they are fixed to the inner side of the strongly-developed socket walls, 

 first under the form of short, slender, converging stems, soon becoming delicate riband- 

 shaped lamellae, directing themselves by a gentle elevating curve to near the anterior 

 portion of the septum, to the sides of which they are attached. The second or upper pair 

 arise on either side of the upper edge of the septum, and extend along its edge to more 

 than half its length, in the form of two triangular anchor-like lamella?, wide at their base, 

 the sides converging to a point ; each lamella forms an inward curve, this process being, 

 most probably, destined to lodge and protect the visceral parts of the animal, leaving on 

 either side a considerable space for the cirrated arms, attached to the under pair of lamellae 

 above described. 



The interior of the larger valve is simple; a central longitudinal, slightly elevated, 

 obtuse projection is seen to extend to about two thirds of the length of the shell, on either 

 side of which, well-defined, elongated muscular impressions are visible, laterally edged in 

 adult individuals by a thickness of the shell, probably occasioned by a superabundance of 

 calcareous matter deposited by a plait of the mantle at the basis of each adductor muscle, 



