~2h.
senticosus Dittmar, as figured by Mojsisovics, and the early Karnian species

Sirenties loczyi Mojsisovics and Sirenites clavigo Mojsisovics are examples.

Sirenites meginae McLearn
(Plate V, figures 1 to 4)
This species has, at various times, been referred to the genera

Steinmannites Mojsisnvics, Meginoceras McLearn, Paratrachyceras Arthaber, and

Sirenites Mojsisovics. It is certainly not a Steinmannites, a Norian genus,
which has eo eatet merres ee to the ventral sulcus and a different suture line,
a suture aie ane resembling Norian Clionites. ane of the name Meginoceras
is deferred for the present, and Sirenites is used in the broad sense.

This species is not a Sirenites in the strict sense, but it shows some
characters of both a Sirenites and a Paratrachyceras. In the nunber of ventral
‘tubercles relative to the number of lateral ribs it is intermediate betweon
Paratrachyoered and Buren test In Paratrachyceras the ribs do not divide near
their ventral ends, so that there is no increase in number of the ventral

tubercles.

Genus Dawsonites Boehm

It has been noted how a new style of ventral ernament appeared in the
early Karnian in the shells included inns genus Sirenites Mojsisovics. At
the same time another new style of ventral ornament avpeared; it was a fission
of each tubercle’ producing paired tubercles in each row bordering the ventral
sulcus. This style of ornament, alone, without further complexity had a short
range, did not survive the early Karnisn, and is a diagnostis feature of the
genus Trachyceras Laube, the genus indicative of the basal cape faunal een
As in Sirenites the sides of the whorl are ornamented with curved oat and rows
of tubercles or spines. The suture line is typically ammonitic.

Boehm (1903) has given the name Dawsonites to ammonoids.with the shell
ornament of. Trachyceras but with a much simpler and ceratitic suture-line.
This genus has been reliably recorded only from the Nathorstites fauna of
northeastern British-Columbila and Bear Island. Johnston has recorded
Brachyceras-with a comparatively-simple suture line from New Pass, Nevada, but

not so simple as that of Paffaonites.