—-23—
attenuated ribs tend to thicken slightly.
Paratrachycoras aylarat is ‘sual ler than | Eatatrachyeoras richthofeni,
Hodeaovice: has coarser ribs, which ure more Sere neihy preqadtedr “thickening
at the ends of ribs is rare and.very slight, and the ventral attentiation of

the ribs is not recorded for P. richthofeni.

_Faratrachyoeras caurinum Nn» Spe ye
| (BL ste VIL, figure 13)
This species briefly degeribed bya the printed cppendix, ie much like»
Pa ratrachyoevas planed n. ena aiid! mey be aay a variety of ite The

ribbing ie suits finer,

. Paratrachyceras tetsa n. sp»
(Plate IV, figures 3,4; Plate VIII,.figure 3.)

Thig species is briefly.des¢ribed in the printed apvendix. The ee a
on the posterior mrt. of the ultimate whorl, preserved, with its even ribbing
ending in tubercles:on the border of the ventral sulcus, is much as in.

‘Pp. dichotomum Muenster, but may be sanewhat Goarlars The irresular ornament...
at the anterior end of the ultimate whorl preserved is very different however,
and unusual in Paratrachyceras». —
Genus Sirenties Mojsisovics:
A-new stvle of ventral ornament in the family Trachyceretidae appeared ..
in early Karnian, that is earliest Upoer Triassic time, and continued.on .
into+the Norian. ©On or. near the ventro-lateral -shoulder-the ribs divide into

short, fine ribs, each;of which ends in.a tubercle; this. means that the

number of tubercles-in the row marginal to. the ventral sulcus-is greater than. -

the number of ribs on-the-sides-of the whorls. All typical species have |;
well-defined ribs and many Lateral rows of tubercles.

In the long, Upver Triassic history of this genus many. new kinds of
ornament, an at eineeione of ornament, appear. ‘The relative number of
ventral tubercles increases} modification of the. ventral tubercles is .
achieved by a braided TL Sa ae and, at maturity, lateral bullae
apvear.-in-some species. The suture line becomes more. complex. Reducéd

ornament at maturity is noted in some species; some varieties of Sirenites