264 
INFERIOR OOLITE AMMONITES. 
longer bend on the ventral area, for tlie ribs meet the carina at an angle of 
about 50°. 
In the adult specimen (PI. XL VI, figs. 1, 2) the ribs are somewhat irregular 
in size ; and they also show some obscure bifurcation occasionally. On other 
specimens there is a tendency towards obliteration of ribbing on the outer 
whorl. 
Tlie carina is generally very inconspicuous, and in some specimens can barely 
be traced. On the end of the body-chamber it is not present either in young or 
old specimens, and the ventral area is therefore regularly rounded. On some 
specimens the carina is bordered by a flat, smooth area each side— this is 
observable in PI. XLVI, fig. 5, and also in fig. 2 on the core. Only one specimen 
(PI. XL VII, figs. 13, 14) has the carina at all elevated, and then it forms merely 
a narrow ridge, bordered on each side by a smooth, narrow area. 
The mouth-horder evidently consists of two spatulate lateral ears, which are 
fairly well developed ; but the ear is not quite perfect in PI. XLVII, fig. 1. In fig. 3 
the mouth is not complete, but the smooth area which lies above the lateral stem 
of the ear is a somewhat peculiar additional feature. This area is not complete, 
and evidently extended farther forwards, but the under part of the mouth — the 
curve springing from the point of contact with the preceding whorl — is quite com- 
plete. It is difficult to imagine what could have been the shape of the mouth in 
this specimen. Fig. 4 shows only the stem of the lateral lappet — the lappet itself 
having evidently been broken ; but the stem is remarkable for the deepness of the 
furrow which it makes on the side of the whorl. The test is present in this case ; 
if it were absent this furrow would not be so remarkable. Figs. 6 and 7 show a 
very peculiar form of mouth. Reasoning by analogy with other genera, it may be 
inferred that this is the form of mouth which aged specimens would possess ; and 
it is present in this small specimen because of a slight injury to the test about a 
third of a whorl back (the scar caused by the injury is just visible on the test) ; 
and the injury has produced decrepitude, bringing about the assumption of senile 
characters at an immature age. 
It is injury, too, which has produced the interesting ornamentation of tlie 
specimen depicted in PI. XLVII, figs. 15 — 17. The ribs are very direct, in 
places thickened or irregular, and in other places bifurcate — all showing some 
disturbance. The ventral area is rounded, but quite on one side is a faint ridge, 
apparently indicating the carina — shifted. On the end of the whorl the ribs are 
distinctly annular, and cross the abdomen in a manner recalling the " Planicosfau 
abdomen " — a character of its ancestor Poh/morjpliifes Vernos[v (Zittel). A partial 
reversion to this form of abdomen is exhibited in the aged examples of this species ; 
but this specimen shows a form of old age even more advanced. Further it illus- 
trates that injury causes premature senility, and that old age causes the production of 
