Hi Thomas, the crust on top isn't ideal, but certainly won't cause permanent harm to your starter. I would probably peel if off if possible, since the dry bits may not hydrate properly.

In future I would recommend covering your starter a bit more securely, so that it remains moist throughout. The reason we say to "cover loosely" isn't because the starter needs airflow in order to ferment properly (it doesn't), but because fermentation gases can build up in a tightly lidded container and cause the lid to pop off. Plastic wrap will flex, and even a lid can work fine, as long as you have adequate space above the starter level for gases to collect, and open your jar now and then to vent the gases. 

Barb

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