Outlex

"ex-lex" means "Beyond the law, outside the law" (OED); lex, then, means "law." It's also an acronym for "lexicon." In this case, I think "outlex" is supposed to mean Shem was an offspring (or outlet) of… but the "lex" part suggests that this connection is outside the law (an outlaw, or, in this case, illegitimate).