I think this may be a fossil from oolitic limestone. does anyone know what type?
It is very small, granted, making one ponder foraminifera, but it is a pentamerous crinoid ossicle.
Here's another example
...And another one much like yours, from the Hunterian Museum Geology Collection, described just as 'crinoid ossicle'
(I give a link directly to the image because the page where it occurs does not want to load.)
Great answer as usual Mike, just thought is it a Pentacrinites ossical?
I can't say for sure. To me, Plantain's specimen shows sectors that are quite well rounded, whereas in Pentacrinites the sectors are often a somewhat oval in shape. But I know that aspect varies within individuals (see this example of Isocrinus dumortieri - http://www.springerimages.com/Images/Geosciences/1-10.1007_s13358-012-0044-9-4) so I can't attach much weight to that. Basically, it is just ambiguous.