Ideas:

1. In the week of Large St Petersburg (Monday) we have two 'sitting' sharks, slightly different from each other. I think the moon has a shark in it, meaning a shadow. Therefore it is not surprising to find a shark here in a calendar for the month. There is a play of light in the moon, giving us notice of when. This glyph (Ea1-17) comes in the 2nd period and in the 1st period we have its opposite (Ea1-9), located in the same position in the period:

2. In my glyph catalogue I have two main types of glyphs showing sharks. The glyph above (Ea1-17) is an example of the main type at left below ('standing up'), the shark-glyphs in Monday are examples of the right main type ('sitting down').

These examples have a general similarity in shape with the main types, but with differences to be read as signs. In Small Santiago we have seen another example, also with signs.