266 
INFERIOR OOLITE AMMONITES. 
of no specimens, intermediate between this species and Dmn. Levesquei, in the 
Murcliisonse- and Opalinum-zones — in fact the MurchisonsB-zone has not yielded 
any species of the genus. 
Although this species is a late survival, yet it is less modified, and shows fewer 
signs of senility than many of the species in the Opalinum-zone. In fact, it is 
reasonable to expect to find descendants of this species in the higher beds of the 
Inferior Oolite. 
Bradford Abbas, Halfway House (Compton), and Louse Hill, Dorset, are the 
principal localities for this species. It also occurs at Stoford, Somerset. 
Though first-named in a Continental work, yet it has not been recorded from 
any foreign locality, and in this respect is like so many of the Goncavum-zone 
species — practically confined to a small area around Bradford Abbas. 
In Plate XLVI are delineated an adult form of this species (figs. 1 — 3), and the 
two ordinary forms met with — the involute (figs. 4 — 5) and the evolute (figs. 6 — 7). 
In Plate XL VII the mouth-border is illustrated in figs. 1 — 7, — a young evolute 
but finer-ribbed form in figs. 8 and 9, — an involute form in figs. 10 — 12, — an abnor- 
mally ribbed form in figs. 13 and 14, — and a decrepit injured individual showing 
atavism or immature senility in figs. 15 — 17. 
PoLYMOEPHiD^ {Continued). 
The genera Polymoephitbs,^ Tmetooeras,^ and Catullocbras. 
The genus Polymorphites is the parent-form not only of Tmetoceras and 
CatvMoceras, but of Dumortieria. As will be seen in the article on the genus, I 
have restricted its scope to include only the direct little-changed descendants of 
Pol. polymorphus. 
Tmetoceras 1 found on Am. scissus, and consider that the ventral furrow which 
is so specialised a character separates this genus suQiciently from GatuUoceras 
with its carina, Tmetoceras and GatuUoceras are collateral branches evidently 
derived from Polymorpliites Zitteli, which has the periodic constrictions, and, 
according to Hang's figure, a certain obsolescence of abdominal ribs ; and the 
latter feature becomes specialised in Tmetoceras more and more until the strongly- 
marked ventral furrow is produced. 
GatuUoceras apparently had something of a ventral furrow in youth. Vacek 
says that " the young of ' Dumortieri ' have ribs very much like those of ' scissus,' 
and that they are broken on the ventral area by a deep, plain, smooth band." (" In 
^ Some of the species which will be placed in these genera have been previously referred to as 
GatuUoceras, p. 232, &c. 
