TEREBRATULA. 63 



examples have not been hitherto obtained as large as the Belgian full-grown type, but 

 this may be accounted for by the reasons already mentioned. 



All our English examples of T biplicata have the beak incurved, with the foramen close 

 upon the umbo of the dorsal valve, so that the deltidium becomes inconspicuous and this 

 seems likewise to have been the case with Brocchi's species, (if we are not misled by his 

 figure), 1 while, on the contrary, in T. tomacensis, and in our Earringdon race, the deltidium 

 is always more or less exposed, and the shell itself is also commonly wider in comparison to 

 its length, than what we observe in the generality of our specimens of T. biplicata. Indeed, 

 some of the Earringdon shells bear resemblance to some young examples of Ter. maxittata, 

 Sow., so abundantly distributed in the Great Oolite of Hampton Cliff, near Bath. When 

 quite young, T. tomacensis seems to be oval, with but a slight trace of biplication, in which 

 condition it bears a great resemblance to many specimens of T biplicata of a similar age. 

 Viscount d'Archiac admits that his Ter. Boemeri, and T. Bouei may perhaps be only 

 varieties of T. tomacensis ; thus their close affinity had not escaped the scrutiny of that 

 learned author. 



The Sponge gravel of Earringdon is as yet our only British locality. On the Conti- 

 nent the species abounds in the Tourtia of Belgium, and in the Upper Green Sand of 

 Mans, (France). 



Plate VII, figs. 11 and 13. Wide examples from the Upper Green Sand of Earringdon, 

 collection of Mr. Morris. 

 „ figs. 12 and 14. Other specimens, fig. 14 exhibiting a very thickened margin. 



,, fig. 14 a . A malformation in the cabinet of Mr. Lowe, in which a very ex- 



ceptional tendency to triplication may be observed. Malformations 

 of this kind may likewise be seen, though very rarely in T 

 biplicata and T. sella, (PL VII, fig. 7.) 

 ,, figs. 15 and 16. Elongated variety. 



Plate IX, figs. 1 to 8. A series of specimens from the same locality, in the collection 

 of Mr. Sharpe, figs. 4, 5, and 7, are referred by that author to T. 

 revoluta, (d'Archiac), and fig. 8 to T. Keyserlingii, (d'Archiac), 2 

 fig. 3 bears also some resemblance to Ter. Tchiaicheffii. 



1 Tins observation had not escaped the notice of the celebrated author of the " Progres de la Geologie,' 

 Mem. Soc. Geol. de France, vol. 2, 2d series, p. 317,1847. 



2 These specimens were obligingly lent to me by Mr. Sharpe, with those names inscribed on his 

 tablets. 



