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Hello all

This is my first post here. I'm an amateur entomologist, with a keen interest in photography.

I'm trying to help a colleague in identifying the suprasquamal ridge on flies. We've got a few key books, but the ridge is often depicted on fairly basic (and frankly confusing) line drawings.

In an attempt to figure out just where to look, I've taken a few photographs of some blow flies in the area we know to be looking, but aren't entirely convinced what we think could be the ridge, is in fact the ridge. If anyone can confirm or point us in the right direction this would be greatly appreciated:

My first attempt, it's not the brownish structure about "8 o'clock" from the base of the halter is it?

Fly 1 by Chris_Moody, on Flickr

Different species, could it otherwise be the structure about 3 o'clock from the base of the halter, with hairs at the bottom?

Fly by Chris_Moody, on Flickr

Different angle, I suspect the calypter may obscure the ridge?

Fly 4 by Chris_Moody, on Flickr

Again, any help will be greatly appreciated, thank you all!