A first group of bats of concern here have only one upper premolar . Premolars are the teeth with points, just behind the canine.
Molars are further back and are relatively flat.
No gap appears behind the upper canine tooth. The second group of bats of concern here have two upper premolars . For us, these include various Lasionycteris, Myotis, Plecotus , and Pipistrellus. If your naked eye could not see the two small premolars, you might think there was a gap there. Well, you have to look close and have pretty good vision in that naked eye of yours.