22 



BRITISH CARBONIFEROUS BRACHIOPODA. 



Spirifeka mosquensis, Fischer de Waldheim. Plate IV, figs. 13, 14. 



Choristites mosquensis, Fischer. Programme sur les Choristite, p. 8, No. 1, 1837 ; 



and Oryctogr. du Gouv. de Moscow, p. 140, pi. xxii, 

 fig. 3 ; pi. xxiv, figs. 1—4, 1837. 

 — Sowerbyi, Fischer. Ibid., pi. xxiv, figs. 5, 6, 7, pi. xxv, fig. 6. (Not 



Spirif. id. Defrance.) 

 — Kleinii, Fischer. Ibid., pi. xxiv, figs. 8, 9. 

 Delthyris incisa, Gold/. German Translation of the Manual of De la Beche, p. 526, 



1832. 

 Spirifer choristites, Von Buck. Ueber Delthyris, p. 45, 1837; and Mem. de la 

 Soc. Geol. de France, vol. iv, p. 191, pi. ix, fig. 16. 



— priscus, Eichivald. Urwelt Russl., Heft i, p. 97, pi. iv, fig. 12, 1840. 



— choristites, M'Coy. Synopsis, p. 130, 1844. 



— Sowerbyi, Be Koninck. Desc. des Animaux fossiles de laBelgique, p. 252, 



pi. xvi, fig. 1, 1843. 



— mosquensis, Be Verneuil and Kexjserling. Russia and Oural, vol. ii,p. 161, 



pi. v, fig. 2. 



Spec. Char. Semi-oval, or of a lengthened semicircular shape, transverse when 

 young, more or less elongated in the adult condition ; valves convex, and somewhat 

 inflated with a rather wide but not greatly elevated fold in the dorsal, and shallow sinus 

 in the ventral valve. The hinge-line is generally as long as the greatest width of the 

 shell ; the area has sub-parallel sides, with a triangular fissure partially covered by a 



pseudo-deltidium. The beaks are incurved and approximate. Ex- 

 ternally each valve is ornamented by from fifty-five to sixty-five 

 narrow, simple, or intercalated radiating ribs, of which from twelve 

 to sixteen occupy the sinus and mesial fold. The ribs in both 

 valves are likewise intersected by numerous concentric lines or 

 ridges of growth, which become the more approximate as they 

 approach the margin. In the interior of the ventral valve a strong 

 tooth is situated on eitherside at the base of the fissure, supported 

 by two large, vertical, shelly plates, which extend from the ex- 

 tremity of the beak to the bottom of the valve, first forming the 

 fissure walls, then converging to diverge again, and extending to a 

 distance of two thirds of the length of the valve. Dimensions variable. 

 Length 22£, width 23, depth 14£ lines. 



Obs. This species has been described to considerable length by both MM. De Koninck 

 and De Verneuil, the last-named author having drawn particular attention to those large 

 dental or rostral plates observable in the ventral valve, which distinguish it from Sp. striata 

 of Martin. These shelly plates or septa have been illustrated in PI. VI of our General 

 Introduction, as well as in pi. v, fig. 2\ of the ' Geology of Russia.' 



The very few British examples of this species which I have been able to examine 



Spirifera mosquensis. 



Interior of the ventral valve. 



S, septa. 



