_~

~19-

The early Karnian svecies, like Protrachyceras hadwigae Mojsisovics,

 P. rudolobi Mojsisovics, and P. subfurcatum Mojsisovics, shared a distinctive

style of ornament with low, broad ribs, bearing clavi, an ornament similar to

‘that in the genus Diplosirenites Mojsisovics.

The shell form of a speci’s in the late Ladinian Daonella shale of Sviti,
Iniia, recalls the shell form of Anisinn Nevadites, and is in contrist with the
more comoressed contemporary svecies. Protrachyceras spitiense Diener has
fairly evolute, stout, whorls, about as hich as thick, with coarse ribs and
large spinate siuhyanemlela 4:

A distinctive style of ornament apoears in the early Karnian svecies
Protrachyceras atavum Mojsisovics, P. schloenbachi Mojsisovios, and P. servile
Mojsisovics. A lateral ornament of mixed soines and tubercles is similar to
that of the species sroup of Trachyceras hylactor, included of course in the
genus Trachyceras. cen enon rane siy ates | |

From early Ladinian to Karnian time, Bevan groups of apacdas) show fewer
rows of tubercles than in the previously noted epoeiear The reduction is
frequently sinncaeal maturity in specimens that have more rows se inner
whorls. The poduecionoscars in what are orovably ae indevendent eroups

of svecies, some orobably representing independent offshoots from the dunni-1

like species. Harly Ladinian svecies like Protrachyceras reitzi Boeckh,

P. chiesense Mojsisovics, P. cholnokyi Frech, and P. recubariense Mojsisovies,
have only one or two rows of tubercles or spines at maturity. They have
fairly coarse ribs, are fairly evolute, and have a ceratitic suture line. The
late Ladinian, evolute species Protrachyceras Julia Mojsisovics and P.
doleriticum Mojsisovics show reduction in number. of rows of tubercles. A
reduced number of rows of tubercles at maturity is also observed in the early
Karnian species Protrachyceras victoriae Mojsisovics and P. thous Dittmar,

The late Karnian species Protrachyceras zenobii Diener also shows fewer rows

of tubercles at maturity than on inner whorls, and has been compared with

12 thous by Diener. Other examples of reduced tubercular ornament will be
considered in describing the genus Paratrachyceras Arthaber.

A few species of Protrachyceras show reduction in, or modification of,
the ribbing, including shortening of ribs, and the assumption of irregular,
uneven ribbing, These soecies include E.? hispanicum Mojsisovics, PR. ibericum

Mojsisovics, P.7 villanovie Verneuil, P.? laricum Mojsisovics and Po? rutoranum