That's an Echinoid, or Sea Urchin (Phylum Echinodermata). We can clearly see the five rows of ambulacral groves and the base of the spines.
Here is an image of a fossil Echinoid, from the Melbourne Museum, for comparison:
Fossil echinoid (sea urchin), Lovenia bagheerae; late Miocene (c. 8 my old), Portland, Victoria
Photographer: Frank Holmes / Source: Museum Victoria
According to the museum:
Victoria contain fossils of many different kinds of echinoderms, including sea stars, brittle stars, crinoids, cystoids, blastoids, edrioasteroids and carpoids. They occur in the Heathcote, Kilmore, Kinglake, Melbourne and Lilydale districts. In much younger rocks of the Cainozoic Era (less than 65 my old), the most abundant echinoderms found in Victoria are the echinoids or sea urchins. They occur mainly in limestones exposed in coastal areas including the Portland, Port Campbell, Torquay, Geelong and Lakes Entrance districts. (emphasis mine)
Your second image, from below, really seems like this image of Lovenia bagheerae:
Source: Museums Victoria