MYTH #1. You can tone your lower abs specifically. There are no separate muscles called "lower" abs. Your "six pack" muscles run from the pelvis to the ribcage, and work as a unit. You can't exercise "just" the lower abs. You can, however, initiate a contraction of your abs from the upper, lower, or side portion of the abdominals. Still, it is more important to supply a strong resistance to the abdominal region than it is to initiate from the specific part you'd like to target. For example, if you perform crunches with a 10-pound weight held behind your head for 15 reps, you will apply a strong resistance to all of your abs, including your lower abdominals. The move will initiate from the upper abs, but your lower abs will still have to work very hard. However, if you perform a reverse crunch with no added weight for 15 reps, while that movement DOES initiate from the lower abs, the total resistance applied to the abs is less and you will get an inferior workout for your lower abs.
MYTH #2. You can pick where you lose bodyfat. Your genetics is the largest determinant for where you lose bodyfat. For both men and women, the fat lying over the lower abdominals is oftentimes the last to go. It WILL come off eventually if you continue to reduce overall bodyfat levels--but not simply from doing more and more lower abdominal exercises, while doing nothing to reduce your overall bodyfat levels.
MYTH #3. You need to do more abdominal exercises if you have a poochy tummy. If you are exercising your abs and reducing overall bodyfat levels according to the recommendations and STILL are not happy with the appearance of your abs, work on your posture, increasing your fiber intake, and decreasing intake of foods that cause bloating before you add ANOTHER set of lower abdominal exercises to your ab routine. And if you're not performing a full-body weight lifting program, make that a first priority!