Drysuit with an adjustable neoprene neck seal.

[Tricky Ricky]

As above.

[pathbrae]

.... wouldn't really be a dry... drysuit

Salopettes style dry trousers and a separate touring cag is the closest I can think of. Kokatat did a roll-together type of seal arrangement so you could join the two together to make a semi-dry suit but an adjustable neck always lets a wee bit of water in so it wouldn't work for rolling, rescue practice or as a survival suit if it all goes wrong.

[jackp]

Sounds a bit like a typhoon hypercurve 4 suit which I recently got as a spare .the neck/arm seals are a neoprene type material and doesn’t seem to be as waterproof even with seals being tight enough .

[Nismosteve]

Typhoon multisport 5. Doesn't have an adjustable neck but it is neoprene and very comfortable. I own one. As already said, an adjustable neck would not be waterproof, if you took a dunking. I have a Palm cag with an adjustable neoprene neck seal. TBH it doesn't vent heat any better than my typhoon drysuit, iff that is your requirement.