was unknown to M. Pictet at the time he published his work, I here append the drawings I made in 1848 from specimens formerly in the possession of the late M. Bouchard, which had been sent to
Fig. 1. — Terebratula diphyoides.
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him by M. Malbos, from the compact limestone of Berrias (Ardeche). I never could see the necessity of burdening nomenclature by the adoption of a distinct generic denomination for these shells; and we should not be zoologically warranted in supposing that because the mantle or lateral portions of the valves have been more or less prolonged, we have therefore valid grounds for the creation of a new genus, any more than we are warranted in separating Orthis biloba, Linn., from the Genus Orthis because the lateral portions of the valves are more or less prolonged in a similar manner to what we find in the deviating lobes of the valves in certain specimens of T. diphyoides, T. viator, etc.
It is very interesting to know that Mr. E. Tawney has discovered a Diphyoid Terebratula in a block of "Oxfordian age" in the Canton de Vaud, and it is most probable that the shell is referable to T. viator; but in that case it would be very necessary that the true age of the block in question should be accurately determined, so as to feel certain that it also might not pertain to the age of the limestone of the Porte-de-France. Nor must it be forgotten that M. Alphonse Favre found a similar specimen at Voisons, near Geneva, which is described and figured in Pictet's work above named. In Switzer-
