Cannot find Arduino under /dev Directory
Note that lsusb does not guarantee the drives are loaded (See https://superuser.com/questions/165733/will-lsusb-and-lspci-list-devices-for-which-the-system-has-no-drivers) 

Per the https://stackoverflow.com/a/14586884/1653571 answer, try an 'lsmod' and see whether you have a 'cdc_acm' module loaded.