Hildoceras (Hildoceras) cf. semipolitum (Buckman 1902)

That's a nice one Roger, although it's a Hildoceras lusitanicum. H. bifrons have a prominent spiral groove in the centre of the whorl.

Just taking another look, I'm pretty sure it's not a bifrons, although it's hard to determine fully whether there's a spiral groove on the outer whorl.

Hi Joe. This time you're wrong, but understandably, since you can't see the groove as well as I can from my point of view.

OK that's a decent sized H. bifrons in that case!

I may be just seeing things, but I'm still not convinced - although I'll happily bow to your superior knowledge. But, have you considered H. semipolitum? It just doesn't look quite right for a typical bifrons. The outer whorls definitely overlap the inner whorls, nearly covering the ribs on the inner whorl - this is more characteristic of H. semipolitum.

Having said that, H. semipolitum is a descendent of H. bifrons and so there are many intermediates.

You're in a position to more accurately identify the specimen, but just thought I'd share my two cents worth.

Okay Joe. I hadn't thought of that one, so I'll have to consider your suggestion seriously. I don't have superior knowledge. I just have the advantage of having it in my hands in 3D. The thing is, there is absolutely no shell on the living chamber and it's a bit beat up to boot, but the more I look at it now, the more I have to agree with you that it's H. semipolitum, which isn't bad at all since I don't have one in the collection yet.

An interesting specimen. Did you find it yourself, if so, where's it from? I'd say judging by the preservation that it's not Ravenscar (which is where H. semipolitum are most frequently encountered). It looks like it could be a Port Mulgrave specimen? I know of H. semipolitum being found there.

Obviously what with H. semipolitum having evolved from H. bifrons there's going to be a whole scale of continuous variation between very clear bifrons, and very clear semipolitum. I'd think this specimen lies somewhat nearer on the scale towards H. semipolitum and therefore I'd assign it as that. However, as you say, things are clearer in the flesh and perhaps there are more 'bifrons-like' characteristics than I can see - in that case perhaps Hildoceras cf. semipolitum would be better?

Either way it's a lovely find, and potentially quite uncommon. I haven't seen many examples of H. semipolitum from Yorkshire, and I am yet to find one…

Do you have a copy of The Ammonite Family Hildoceratidae in the Lower Jurassic of Britain - by M. K. Howarth? There's some good information in there about the different species. If not drop me a PM and I can send you an extract on Hildoceras.

Thanks again for your interest. I got it on a trade with David Bundock, "Bunders" in the UK Forum...that is to say, he spontaneously offered me a parcel with a few things in it and this came along as a nice surprise. I just sent him something in return for the nicety. He couldn't tell me any more than that it's from "Whitby" and wasn't any more specific about it, so I suppose he might have got it on a trade as well. I have the impression he doesn't pay much attention to details if it's not a vertebrate.

Anyway, I was also thinking of making a "cf." out of it, so I guess that's about as far as we'll get. Yes, I do have Howarth's tome, but thanks anyway for the offer.

Ahhhh OK. That sounds like a good identification to me, well played..