First up is this odd looking piece which I believe is the interior of a pedicle valve from a strophomenid type brachiopod.It has the characteristic half-moon shape and I think that the relief seen near the one side of the fossil represents some muscle scars.
Next is this Graptolite which may only be a part of a larger colony. The rounded end does look like it is supposed to naturally occur like that but the other end seems to have extended farther at one time.
Lastly is this cast of a cephalopod. It is interesting because of the slanted or spiral like pattern. This could be an impression of the exterior decoration of the shell rather than the usual internal vertical chambers. Three sides are preserved with the fouth filled with Calcite.
Hopefully I'll get some more fossils from the St. Petersburg region in the future. I don't have enough to really compare to those that I've found in here in the US or Canada.
I think your cephalopod is the siphuncle. Endoceras has a siphuncle like this.
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