The 1892 RLDS edition accidentally replaced the sentence-initial now with and. There was no reason for emending the text here. Nor does the 1892 edition (the second RLDS edition) generally involve much editing; that edition is basically a copy of the first RLDS edition (1874). Yet this 1892 typo has been retained in the RLDS text. The preceding sentence (in verse 10) begins with “and it came to pass”; this is the probable source for the 1892 replacement of now with and in verse 11.
Summary: Maintain the original sentence-initial now in Mosiah 19:11.