TEREBRATULA. 57 



figs. 33 to 44, are examples. This form approaches most to the Italian figure, and should 

 be looked upon as the more typical shape. M. D'Orbigny's illustration, Pal. Eranc, 

 Terrains Cretaces, vol. iv, PI. 511, figs. 5, 6, 7, is likewise referable to this form. Ter. 

 faba, Sow. is simply a dwarf Terebratula biplicata from the Upper Green Sand of 

 Warminster. 1 



2. Those wider and more flattened shapes commonly met in the Gault of Folkestone, 

 and Upper Green Sand of Cambridge, (PI. VI, figs. 1 to 9, 12, 29, &c.) in these the two 

 plaits are much more widely separated, and to it, M. D'Orbigny's illustration, Pal. Eranc, 

 PL 511, fig. 1, may likewise belong. This is the variety I had intended to retain as Ter. 

 Dutempleana (p. 53) and No. 1, as Ter. biplicata, (Brocchi,) a view I now abandon for 

 the reasons already specified. 



Ter. obtusa, Sow. (PI. VI, figs. 10, 11, 13, &c.) is only a variety of Ter. biplicata, 

 or Dutempleana, in which the shell has extended more in width than in length, and 

 wherein the biplication has either entirely disappeared (figs. 10, 11,) or exists simply in a 

 rudimentary state, (figs. 13, 23), but that this is simply an unusual condition of the 

 species has been amply proved by a series of upwards of a thousand examples collected 

 by Mr. Carter, at Cambridge, and in which every passage may be traced uniting such 

 extreme forms as fisrs. 3, 6, and 10. 



It seems difficult, in the actual state of our knowledge, to specify with certainty the 

 precise period at which Ter. biplicata made its first appearance, but, if some shells (PI. 

 IX, fig. 40) lately discovered by Mr. Mackie in the highest bed of the Lower Green Sand 

 series at Eolkstone, really belong to this species, they would be the oldest examples with 

 which we are acquainted. 



Ter. biplicata occurs in the Gault of Folkstone, the Speeton Clay of Yorkshire ; and 

 the red chalk of Hunstanton ; it abounds in the Tipper Green Sand of Cambridge, in the 

 neighbourhood of Warminster, at Earringdon ; and although less common, still seems to 

 be represented in the Chalk marl and Lower Chalk of Cambridgeshire : — thus having a 

 wide vertical range, extending almost through the entire cretaceous system. 



On the Continent, it occurs at Wissant, in the Gault, and in many of the Upper Green 

 Sand localities of Europe. 



Plate VI, figs. 1 and 2. Ter. biplicata var. Dutempleana, D'Orb. from the red chalk of 

 Hunstanton, in the Collection of Mr. Pitch. 

 „ figs. 3, 4, 5. A large specimen from the Upper Green Sand of Cambridge, 



in the Cabinet of Mr. Carter, 

 fig. 6. A remarkable example from the same locality and collection, showing- 

 traces of coloration. 



1 Professor Forbes states, in his catalogue of the Lower Green Sand fo^ils, Quart. Journ. Geol. Soc, 

 vol. i, p. 346, "T.faba (Sow. in Fitton, t. xiv, fig. 11). The original specimen is in the Geological Society's 

 collection, and is from the Upper Green Sand of Warminster ; it appears to 'oe a young or starved state of 

 T. biplicata, or some allied soecies." 



