=20-
Mojsisovics. The species Protrachyceras ladinum Mojsisovics and P. gredleri,
already mentioned, grew to a large size, sat atte lost most of their
ornament. Boseibly this mature stage wag Len ia some Renee Be eiene but
the adult shells eS ava been vreserved. i
Strigate ornament appears in a group of Wage of Protrachyceras in
Ra)
Shasta county, California, and in late Karnian time, when species referred to
this genus made their nae appearance. This distinct group includes

Protrachyceras lecontei Hyatt and Smith, P. shastense Smith, P. madisonense

Smith, Pe dnaerent Smith, P. beckeri Smith and P. californicum smith, all
from the Hosselkus limestone. They have compressed to stout whorls, and bear
a peculiar ornament, including a stage of rather coarse ribs, succeeded by a
stage of more delicate ornament with very fino ribs, gronaca by Lonai tudinal
ridges or mince bearing very fine tubercles or very fine eulles: They Bee
all fairly Seas and Haven ecoler cut suture lines with ase saddles and
long lobes. These svecies anpear to have the most elaborate Bene lines of
those referees to Protrachyceras. The suture lines of Anisian and Lad inian
species are mostly serati tive rarely subammonitic or weakly ammonitic.e Very
few suturg lines of early Karnian species have been prepared; they ae all

ammonitic.

‘Protrachyceras sikanianum McLearn
ae Near “>. QPlate I, Figures 2 to5)

Of the many styles of shell onntnentdn Ladinian and Karnian time,
described above, three are represented in-the Nathorstites fauna of north-
eastern British Columbia, two in the species Protrachyceras sikanianum and
one in-Protrachyceras zauwae. ean hay

It has been siyenoed! how in late Ladinian time, clavi mirginal to, and
parallel with, the ventral. sulcus appeared in species like Protrachyceras
pseudoarchelaus Boeckh and in the early Karnian species _P. aeoli Mojsisovics.
Varieties of P. sikanianum without lateral bullae are in this category. ‘They
differ from P. pseudoarchelaus in being a little more involute and in having
one row less of tubercles and a simpler suture line. They differ from P. acoli
in having fewer rows of tubercles and in being somewhat more involute;
unfortunately the suture line of P« aeoli is not kmown.

-- .!. The appearance of lateral bullae at maturity, together with the marginal

_ clavi parallel with the ventral sulcus in the late Ladinian species