Dating Ptolemaic silvers?

[AETHER]

Hey, if anyone could shed some light on how dating Ptolemaic silvers goes, as specially the ones the use Ptolemy I on the obv.

The simplest explanation will be appreciated.

Ptolemaic coins have grabbed my interest but having some issues understanding how to determine a Ptolemy II from a Ptolemy VI for example, they all seem very similar.   Ptolemy I on the obv. Eagle on Reverse, king title, etc.

Is it weight and style? Hoards found? 

Were Didrachm's produced later? 

Thanks.

 

[Edessa]

CPK just shared this over in the topic on online references:

http://numismatics.org/pco/

[NewStyleKing]

I once had a Ptolemy ll  . Svoronos, I think said the y between its legs gave a date but I understood  that was shown to be wrong...where this info (EVER) comes from is a mystery like the changing of the seasons and the tides of the sea.....

 

Ptolemy ll Philadelphus Tetradrachm 283-246 BC 

Obverse-Head of Ptolemy l Soter wearing Aegis
27.49 mm 14.24 gm
Struck in Alexandria after 275 BC
Rev- Eagle with closed wings clutching thunderbolt.
Left field, Σ , Galatian shield
ΒΑΣΙΛΕΩΣ ΠΤΟΛΕΜΑΙΟΥ
Y between eagles legs

[kirispupis]

Here's mine. I believe the main reference for these coins is Lorber - Coins of the Ptolemaic Empire. I've been tempted to pick up a copy, but there are very few Ptolemaic coins I'm after so it's tough to justify the expense. This one happens to have a date mark, which is typically of the Phoenician cities.

Ptolemaic Kingdom of Egypt, Ptolemy II Philadelphos
AR Tetradrachm. Tyre, dated RY 30 = 256/5 BCE
14.01g, 25mm, 12h.
Diademed head of Ptolemy I to right, wearing aegis around neck / ΠΤΟΛEΜΑΙOΥ [BAΣΙΛEΩΣ], eagle standing to left; monogram of Tyre above club to left; Λ (date) above monogram to right; A between legs.
CPE 577; Svoronos 657; SNG Copenhagen 488; DCA 20
Ex collection of R. N. Draskowski;
Ex Ephesus Numismatics, North Carolina, USA