Epson, being a total douche, does not provide a scanner driver for the DX3850 for OSX.
The printer driver comes (as almos any printer driver known to man) bundeled with OSX, but for the scanner you have to rely on the TWAIN SANE Interface for MacOS X

First install libusb, then the other packages. Now you should be able to e.g. use the image capture utility to do your scans.

Works like a charm.