PLIENSBACHIAN (LOWER JURASSIC) BIOSTRATIGRAPHY AND ...

40
35
30
25
20
15
10
35
30
25
20
15
10
35
30
25
20
15
10
Dubariceras freboldi
------------F--------1------1---- 1----1---1---1--1---
2 3 4 5 6 7 8 9 10
—i------1---- 1----1— i—i—i—
4 5 6 7 8 9 10
—i----1— i—i—i—
6 7 8 9 10
UD (mm)
Dubariceras silviesi
20
20 40
—I—
20
“ i----------------- 1------------ 1---------- 1--------1— i— i— i
40 60 00 100
40
- I ----------- 1--------- 1— i— i— i
60 80 100
—i----1— l—i—•
60 80 I00
? 75. O rnam entation envelopes fo r species o f the genera Dubariceras and Metaderoceras.
mary ribs per h a lf whorl (P R H W ) are p lo tted as a fu n ctio n o f umbilical diam eter (UD).