"Dek" and "El", based on the Greek for 'ten' and 'eleven'. Other notations may use T & E, X & L, or 2 & 3 flipped upsidedown which I dislike the most.
I've no clue what the conventions are, but I suppose you could say their numbers as "dek-teen", "elty-six", "dekty-eight", etc.
Link
Meg James
This is very cool! Stuff like this has always confused my base-10 brain but this graphic definitely makes it a little easier to comprehend.