201 
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described, after W. Martin, as follows: — T. hastata, by J. Sowerby; T. 
hovidens, by Morton ; T. vesicularis and T. liastceformis, by myself ; T. cymhcB- 
formis, by J. Morris ; T. amijgdala, by J, D. Dana; T. fiisiformis, by E. de 
Verneuil ; T. Gillingensis, by T. Davidson, &c. 
Leopold de Bucli was the first to admit that all the varieties figured 
under these different names were of one and the same specific type, and were 
connected by such insensible gradations that it is difficult to define them. 
The same opinion was given by me in 1843, and by E. de Verneuil in 1845. 
It was after long hesitation, and after comparing a considerable number of 
specimens from different countries and localities, that my learned friend Mr. 
T. Davidson accepted the same view. I must, however, mention that, in 
some localities, one or other of these varieties affects a constant dominant 
form, so that there is little wonder that it should so long have been considered 
a distinct species. Thus, for example, the typical form figured by W. 
Martin, is chiefly found, and often in great abundance, in the Upper Car- 
boniferous beds of Vise and Namur, Belgium, of Settle and Bolland, England, 
of Glasgow, Scotland, and of Cork, Ireland. It is much less frequent in the 
middle beds, as at Waulsort, near Dinant ; and it is nearly completely 
replaced by the variety T. hastata, or forms approaching it, in the lower beds 
of Tournai, Belgium, Hook Point, Ireland, and Burlington, America. 
Although both of the chief varieties are represented in Australia the T. hastata 
predominates, and is most frequently met with. It is in this variety that 
T. cymboiformis, J. Morris, and T. bi-undata, McCoy, ought to be placed. In 
order to render the definition of the species more correct, and to facilitate its 
exact determination, I have figured the principal varieties found by Mr. 
Clarke, and, like Mr. Davidson, I have described them separately. 
Variety 1, having for its type : 
Terebratula saccules, Martin. 
PI. XV, Pig. 5. 
This is usually rather small, oval or sub-pentagonal, a little longer 
than broad, with folded front ; its valves are nearly equally convex. The 
ventral valve is supplied with a ventral furrow very pronounced towards its 
frontal extremity, while its dorsal valve is only slightly impressed in the 
corresj)onding part. The surface is smooth, or simply ornamented with a 
