—18—

cents creer ent

‘Pe margaritosum iojsisovics and the late Ladinian P. anatolicum Toula,

P. EAA Garone lade mecckhy iE steinmanni Mojsisovics, and the inner whorls
of P. ErOAtenl veqeieonice Of the above, P. lahontanum Smith and P.
americanum in the Anisian of Nevada have stout, low, evolute whorls. and
coarse ribs like Nevadites, from which Protrachyceras is said to have
oricinated ‘or at least to which it was closely related in Anisian time.
Protrachyceras ansoni Diener from the Tropites limestone of Byans, India,
aopears to have similar ornament, but is much more involute than any other
species of Protrachyceras.

In some soecies of Anisian, Ladinian, and early Xarnian time the
tubercles of the ventral rovs marginal to the ventral sulcus, one on either
side, became modified to form clavi parallel with that sulcus. Clavate—like
ventral tubercles first aopeared in the Anisian Pe ene A eeleie at maturity.
From illustrations it is inferred that these ventral clavi appeared in the

late Ladinian species Protrachyceras ladinum Mojsisovics and P. longobardicum

Mojsisovics and in the early Karnian P. aeoli Mojsisovics. They also seem to

have avveared in the early Karnian Protrachyceras attila Nojsisovics and
related svecies, including P. medea Mojsisovics, Ps thyrae Mojsisovics,

P. arion Mojsisovics and PaiuaoouienniMoqeiaovies: this group has the
additional distinctive character of an increase in number of ribs and number
of rows of tubercles over and above those in the dunni group and a ove the
other nea with ventral clavi.

The simole ornament of the dunni group of soecies also became modified
in another way in a few species. Small lateral bullae, with some reduction
in strength of ribbing, apvedred at maturity in the late Ladinian svecies
Protrachyceras longobardicum Mojsisovics and in the early Kernan scecies
ene oedipus Mojsisovics and P. cassiovela Mojsisovics. Drips
longobardicum, as already noted, the ventr«l tubercles were modified to form
clavi. In the other two species the ventral eecoles remained. unmodified.

The ornament of the simoly tuberculate species group of P. dunni became
modified in yet another way. The tubercles became somewhat produced and
- assumed a spinate form. Spinate capenates apoeared in the late Ladinian
Protrachyceras archelaus Laube and in the early Karnian Protrachyceras
septemspinatum Mojsisovics. Spinose tubercles also a dvear in other groups i

of species and will be referred to later.