TISSOTIID®. 43 
SUBTISSOTIA n. gen. Hyatt. 
This group includes a number of the species heretofore associated with 
Tissotia tissoti on account of the sutures. These are unquestionably similar 
in the simplicity of their outlines, but, as has been argued above, this fact 
can not be considered as determinative in such peculiar retrogressive 
groups, unless correlatable with other characteristics and especially with the 
changes in the development both of the young and the gerontic stage. 
The younger stages, so far as known, beginning with the neaniec stage, 
have, as a rule, very globose forms with continuous keels, the sides are 
costated and terminate outwardly, with tubercles that form raised but 
discontinuous ridges on either side of the keel. The venter is much 
broader than the area included within these lines of nodes, except in the 
gerontic stage, when it narrows down to the same limits as are common in 
Metatissotia. The keel disappears in the gerontic stage and the lateral 
coste and the nodes also in some species, according to Peron’s figures, 
leaving the venter more or less rounded. 
Type is Subtissotia inflata (Peron). 
SUBTISSOTIA INFLATA (Peron). 
Tissotia tissoti var. inflata Peron, 1897, Mém. Soc. géol. France, Paléontologie, 
Vol. VII, No. 17, pl. 19, fig. 6. 
The figures of this form, given by Peron, show an excessively stout 
shell, increasing rapidly in transverse diameters by growth, with an 
obtusely subacute venter, prominent keel, and slight channels on either 
side, bordered by ridges. Peron’s figure at diameter of 68.5 mm. is 51 mm., 
while the figure of intermedia, which is 92 mm. in diameter, is 53 mm., only - 
3 mm. wider than the much smaller and younger specimen of inflata. Such 
differences of proportion do not occur in the same species of Ammonites. 
Locality: North Africa. 
Age: Base of Senonian. 
SUBTISSOTIA INTERMEDIA (Peron). 
Tissotia tissoti var. intermedia Peron, 1897, Mém. Soc. géol. France, Paléontologie, 
Vol. VU, No. 17, pl. 12, figs. 4, 5. 
Tissotia tissoti var. levigata Peron, ibid., pl. 13, figs. 1, 2. 
This form differs from inflata in having much less gibbous volutions at 
the same age and a more acute venter at all stages. 
