Distinction between defenses in abatement and on merits is that abatement of a pending action does not bar a future action on the same cause.  But a judgment on merits concludes the action.  The plea of another action pending is a plea in abatement.[i] The defense of abatement because of the pendency of another action is dilatory and technical in nature.[ii] The plea that the plaintiffs did not allege compliance with a requirement for a notice of claim, that they are unable to prove such compliance and that they could not recover regardless of the label placed on the plea by the pleader is a plea in bar and not in abatement.  The defense in abatement is intended to defeat the particular action because the action is improperly brought and does not go to the merits of the cause of action.  Allowance of this defense amounts to a dismissal without prejudice of the abated action.  The party asserting the defense must clearly show that s/he is within the reason for its enforcement.  A plea in abatement is strictly construed as to its effects.

[i] Stephens v. Monongahela Bank, 111 U.S. 197 (U.S. 1884)

[ii] Moresca v. Allstate Ins. Co.,231 So. 2d 283 (Fla. Dist. Ct. App. 4th Dist. 1970)