Now the sons of Saul were Jonathan, and Ishvi, and Malchishua; and the names of his two daughters were these: the name of the firstborn Merab, and the name of the younger Michal:
As cited earlier in this chapter, the omission of the name of Isbosheth, or Eshbaal, from this list of Saul's children is probably due to the fact that this list was written very early in Saul's reign, before Eshbaal was born.  Abner made Eshbaal king over part of Israel following Saul's death; and he contested with David for the throne of all Israel for a period of seven years.  The significant fact  (2 Samuel 2:8-11) of Eshbaal being forty years of age when he was declared king is the basis for concluding that Saul reigned forty years.  The theory that Ishvi is the same son as Eshbaal is an ingenious device to avoid the deduction regarding the length of Saul's reign.