The forcipular teeth can be seen along the anterior edge of of the coxosternite that lies between the forciples (jaws) (see image top right). These lie below the head and need to be viewed from below.
The smaller Lithobius species (up to 15 mm body length) usually have 2+2 forcipular teeth (rarely a third on on side) (image far left). As do the similar looking Lamyctes species.
The larger Lithobius species, even in small immatures, have at least 4+4 forcipular teeth (often several more) (image botton right).
Thus it is straightforward to decide if a small specimen is an adult of a small species or (as is often the case) just a small immature of a larger species.