Found loose and already broken at Cayton Bay Scarborough.
Matrix of ooliths about 0.4mm.
Grid of 1cm squares
Referred to plate 33:2 in British Mesozoic Fossils, Natural History museum, British Museum.
Plate Very similar to my find except that the rate of increase in whorl fattening is greater than illustrated.
Lateral tubercules correct. However every photo I've seen of M. macrocephalus has no tubercules.
Is it what I've found in the book? The book was published in 1975.