...it usually means the ID is sound; it's when it says otherwise that we should exercise a lot of caution

thanks for the good job, James.

Yeah it seems testiculatus is definitely the more uncommon given that it is not mentioned anywhere at all, not even on BOLD.

It specifically says obliquus is black and shining with brownish hemelytra which is specific among the genus (which applies to all the bugguide ones for Cal). So I take it testiculatus is NOT black and shining with brownish hemelytra. If so that makes these guys pretty easy without the specimen.

I didn't assume the colouration was different between the two when keying it out though, just to make it clear I didn't jump to conclusions!

What details would help?

...so please try the key to spp. (2 in CA) on p.401(1) and see what transpires; shouldn't be hard with the specimen

I'm looking into it. That document is extremely cumbersome to navigate and crashes my computer every time I try and change pages (it has taken me over an hour to get to page 401), but its good that it exists. I'll reply again if I work it out.

did you download it, or just trying to read online? [i never do the latter]

My computer isn't great though.

Do you know what page figure 90a-d are on? That apparently has the clue to distinguishing these two species via something called the osteolar peritrome. (It is "smaller" on testudinatus, compared to "larger" on obliquus)

unfortunately, the grainy digitized version has messed up those fine drawings beyond recognition, so the plates are hardly of any use :/

now the question is where is that on the insect itself, presumably on the underside somewhere...It says obliquus is "piceous" overall with alutaceous corium and hemielytra, which is apparently distinctive in the genus (these details fit my bug). But it does not say how testiculatus looks colour wise in comparison.

EDIT: presumably in the area this image was taken, which seems to confirm my suspicion of where it is: