66 BRITISH CRETACEOUS BRACHIOPODA. 



Sowerby is certainly in error while supposing that the same shell was common to the 

 Chalk and Cornbrash. Baron V. Buch, and others, have likewise erroneously added to 

 their synonyms of T semiglobosa, the T. intermedia (Sow.), a Jurassic species, distinguished 

 by shape and character. 



Sowerby mentions that, in the true type of T. semiglobosa, the frontal margin is 

 slightly " undulated with two risings'' or plaits ; but after inspecting a series of several 

 hundred specimens from the Lower Chalk of Lewes, Chardstock, and other localities, it 

 appeared evident that the front was at times almost straight or arched, without any defined 

 biplication, and it was from shells presenting this last condition, that Mr. Leymerie 

 founded his T. albensis} T. semiglobosa is also distinguished from T carnea (Sow.), this 

 last being a much more depressed shell, with a uniform straight margin, a character 

 observable only in young examples of the species under consideration. And it may be 

 worthy of notice, that we rarely find both forms associated in the same bed or locality ; 

 where the one abounds the other seems wanting : thus, in the Upper Chalk of Norwich, 

 Brighton, Meudon, &c, where T. carnea is common, T. semiglobosa is absent ; while the 

 inverse takes place in the Lower Chalk of Lewes, Gravesend, Chardstock, &c. 



Ter. bulla, Sow., figured in pi. xxxii, of Dixon's work, is also only an unusually 

 large and more elongated form of T. semiglobosa, possessing no other valid distinguishing 

 feature. 



The vertical range of this species appears to be greater than that of Ter. carnea ; we 

 first find it in the Red Chalk of Hunstanton, believed by some geologists to represent the 

 age of the Gault : it abounds in the Chalk Marl and Lower Chalk of Lewes, Charing, 

 Gravesend, Tytherleigh, Chardstock, and other localities. On the Continent, it is very 

 common near Rouen, in the Dep. de PAube, &c. 



Plate VIII, fig. 6. Ter. semiglobosa, from the Lower Chalk of the neighbourhood of 



Lewes (Sussex). 

 „ fig. 7. „ from Gravesend. 



„ fig. 8. ,, a remarkable variety, from Lewisham (Kent). 



„ fig. 9. „ Sowerby's original figure of T. subrolunda ; 



specimens very similar to this may be col- 

 lected near Lewes. 

 „ A large example from Lewes, in the collection 



of Mr. Catt. 

 „ another specimen (T. bulla, Sow.), in the col- 



lection of Mr. Wetherell. 

 „ a specimen from the Chalk of Grays, in the 



cabinet of Mr. Morris. 



1 Ter. albensis is supposed by Prof. Bronn and M. D'Orbigny to be a variety of T. obesa, but the 

 proportions of the foramen in the two forms is so different, as hardly to warrant such a conclusion. 



fig. 



10. 



fig- 



11. 



fig- 



12. 



