The author shows that the congruences K3, referred to one of its focal surfaces, which are bases for the construction of a complex with a triple inflection centre on each ray, exist with arbitrarinness in one funct'on of two arguments.
On each surface with arbitrariness in three functions of one argument there exists a one-parameter family of curves which are focal curves of some congruence K3, referred to this surface.
It is shown that with arbitrariness in six functions ol one argument there exist congruences K3 referred to both their focal surfaces.
Citation Example:Kovantsov N. I. On a Projective-differential Class of Congruences // Ukr. Mat. Zh. - 1960. - 12, № 3. - pp. 257 - 266.