Updated.
No subtype on this one?
Yes, these look like no-subtype dragons.
Environment: Any coastal land?
These live in the water to, so I was thinking more:
Environment: Any coastal aquatic or coasts and islands
Treasure: x (Obviously, lots and lots of pearls)
Treasure: Triple standard (all gems are pearls) ?
CR and LA could be tricky on this one. Although it has less HD than most other true dragons, its spellcasting rivals the best metallics.
Well that suggests their CR should be somewhere in between, maybe the average of a White Dragon (for the weak physicality) and a Silver Dragon (for the powerful spelluse)?
White Dragon: Wyrmling 2; very young 3; young 4; juvenile 6; young adult 8; adult 10; mature adult 12; old 15; very old 17; ancient 18; wyrm 19; great wyrm 21
Silver Dragon: Wyrmling 4; very young 5; young 7; juvenile 10; young adult 13; adult 15; mature adult 18; old 20; very old 21; ancient 23; wyrm 24; great wyrm 26
Averaging them would work out:
Pearl Dragon: Wyrmling 3; very young 4; young
5-6; juvenile 8; young adult
10-11; adult
12-13; mature adult 15; old
17-18; very old 19; ancient
20-21; wyrm 21-22; great wyrm
23-24
Hmm, if we use that at a baseline and add a minimum CR of caster level +6 that might be better. It'd give us:
Pearl Dragon: Wyrmling 3; very young 4; young 6; juvenile 8; young adult 10; adult 12; mature adult 15; old 17; very old 19; ancient 21; wyrm 23; great wyrm 25
That looks about right, it gives it the biggest jumps in CR at Young (when it first gains spellcasting) and adult (when it becomes Large).