All depends in what are your aims for your study (statistial study of the variability? evolutionary trends? etc.), and which diagrams you want to make (univariate? bivariate? multivariate ACP?, etc.).

Usually, and basically, I use some classical measurments: D (diametre), H (height of the whorl), W (thikness of the whorl), U (umbilical diameter). And for the ratio: H/D, E/D, U/D, E/H and U/H.

You should also consider the ornamental dimensions (number of primary/secondary ribs, tubercles per whorl or 1/2 whorl, etc.).

All these are the "basical" dimensions. Other are sometimes usefull (retroversion of the ribs, suture line complexity, septa number per whorl, etc.)...

Dear Didier

Ok.Very very good.thanks a lot.

I work on systematic and paleoecology on Toarcian-Bajocian Ammonites.

I draw diagrams of some specimens. What interpretation can be found in the diagrams? 

Please look at my diagrams and help me. very very thanks

There are no diagrams in the file you shared, only raw data. However, the problem you'll have is the robustness of the results with only seven measurement sets of Emileia (the confidence level is of about 35-40)...

Diameter, whorl height, umbilical width and the whorl height at 1800. are the most important measurements. One can measure the change in the umbilical width in excentric umbilici and the rate of increase of the whorl height. The thickness of the whorl and the involution of the outer whorl over the penultimate whorl are less important measurements. Measure in two direction first the largest diameter and seconly the measurement at 900.