268 
INFERIOR OOLITE AMMONITES. 
were many offshoots. Now, Dr. Haug had extended the genus PolymorphiUs 
to include many of these offshoots, notably Amm. Bronnii, confusus, &c. ; and 
it was, at first, my intention to have left the genus, say for the Amm. Bronnii 
series — in which it appears to me Am. Jamesoni should be included, and to 
erect a new genus for " Vernosse " and its allies, removing them from Gatullo- 
ceras. This, however, would have been opposed to the best aims of nomenclature, 
which is to keep the older generic name for the radical stock, and apply the newer 
names to the various offshoots ; and, as Dr. Haug writes to me that he is now of 
opinion that " Vernosse," &c., and "Jamesoni" ought to be placed in Polymor- 
phites (personally I am doubtful about "Jamesoni"), I shall retain Polymorphites 
for the radical stock, and leave others to settle the position of the more-developed 
branches. Am. Jamesoni, &c. 
Polymorphites, then, restricted in this sense, begins with Pol. polymorplms 
— which, by the way, is probably an evolute development of " Cymhites " glohosns, 
and is probably not genetically connected with Agass. miserabile, as Haug suggested 
and I mentioned (p. 232), though it resembles it very closely — and among other 
branches throws off Am. Bronni leading to Am. Jamesoni. Keeping, however, to 
the radical stock — the forms with uninterrupted annular ribs — there is in the 
Middle Lias Pol. Vernosse (Zittel),^ an apparent development of Pol. polymorphus 
costatus ; and from Zittel's species by slight mutations are derived Pol. Zitteli' 
(Haug) in the Upper Lias, Pol. norma^ (Dumortier) in the Opaliniim-zone, and 
Pol. senescens, n. sp. It is only with the latter that I am concerned. 
Polymorphites senescens is most interesting, because it is evidently a senile form 
of this radical stock. It retains the primitive form of ribbing, and yet shows its 
senility so clearly in its compressed involute whorls. 
PoLTMOEPHiTES SENESCENS, 8. Buclcman. Plate XL VIII, figs. 13 — 15. 
Discoidal, compressed, uncarinate. Whorls ornamented with annular to sub- 
annular ribs which cross the abdomen. Ventral area not defined, crossed by 
straight ribs. Inclusion about one-quarter. Suture-line simple. 
This interesting little species, which is evidently a degenerate senile form 
(hence the name) of the radical stock from which Tmetoceras, Gatulloceras, and 
Dumortieria sprang, is noticeable for its primitive character, and the late time 
^ " Geol. Beobactungeu Central-Ap. ;" ' Geogu. Pal. Beitriige,' Bd. ii, Heft L', pi. xiii, fig. 5, 1S69. 
2 " Polymorphidse ;" ' Neues Jahrbuch fiir Mineral.,' Bd. ii, pi. v, fig. 2, 1SS7. 
3 ' Etudes pal. Bassin Rhone,' iv, pi. Ivii, figs. 7, 8. 
