It sounds like you're referring to a — likely a USB mass storage device that uses an MSdc (Memory Stick Duo Card?) or similar flash interface internally.
GenPlus USB-MSdc Disk USB Device
/dev/sda1 /mnt/genplus vfat defaults,noatime 0 0 (Replace /dev/sda1 with actual device node.) genplus usb-msdc disk a usb device