70 BRITISH CRETACEOUS BRACHIOPODA. 



Plate VIII, fig. 3. A lengthened variety, T. elongata, Sow., from the Chalk of Norwich, 



in the cabinet of Mr. Eitch. 

 „ fig. 4. A large circular variety from the same locality, in the collection of 



the Rev. T. Image. 

 „ fig. 5. Another example from the same locality. 



29. Terebratula depressa, Lamarck. Plate IX, figs. 9 — 24, 



Terebratula depressa, Lamarck. Hist, des An. sans Vert., vol. vi, p. 249, 1819, ' 



and Dar. Notes on an examination of Lamarck's species of 

 Fossil Terebratula, Annals and Mag. of Nat, Hist., vol. v, 

 2d ser., pi. xiii, fig. 15, 1850. 



— ovalis, Morris. Quart. Journal Geol. Soc, Nov., 1846 (not T. ovalis, 



Lamarck). 



— Nertiensis, If Archiac. Mem. Soc. Geol. de France, vol. ii 3 2d ser., 



p. 313, pi. xvii, figs. 2—10, 1847. 



— viQUESNEiii, If Archiac. lb., p. 316, pi. xviii, fig. 1. 



— depressa, Bronn. (part). Index Pal., vol. ii, p. 1234, 1848. 



— — D ' Orbigny ■. Prodrome, vol. ii, p. 172, 1850. 



— — Sharpe. Quart. Journ. of the Geol. Soc, vol. x, p. 191, 1853. 



Diagnosis. Shell depressed, oblong oval, tapering at the beak; valves almost equally- 

 deep, externally smooth, and marked by a few concentric lines of growth. Dorsal or 

 socket valve either regularly convex or interrupted by a mesial fold of moderate elevation ; 

 ventral valve with, or without, a shallow longitudinal depression ; beak nearly straight, 

 more or less produced, and truncated by a large circular foramen, partly margined by a 

 wide deltidium, in one piece ; beak ridges undefined, lateral margins moderately flexuous, 

 frontal edge of the ventral valve indenting to a greater or lesser extent that of the dorsal 

 one. Loop short and simple, not exceeding a third of the length of the smaller or dorsal 

 valve. 



Dimensions variable : length 22, width 17, depth 14 lines; 



,, 20, ,, 20, ,, 11 ,, 



Obs. This Terebratula is one of our largest Cretaceous forms, varying very consider- 

 ably in shape and comparative dimensions. When quite young it is much depressed, with 

 the margins straight all round; but with age, the valves either continue to remain 

 regularly convex without any defined mesial fold, or with one of moderate elevation. The 

 beak is also more or less produced, and at times much elongated, with a large deltidium 

 bearing resemblance to that peculiar to Ter. longirostris of Wahlenberg; but the 

 Lamarckian species seems separable by its greater width, and by the almost total absence 



1 " T. testa oblonga transversim dilatata, supra coarctata et obtusa, striis concentricis latvibus ; nate 

 producta non incurva : for amine magno." 



