That’s straightforward. None of the Paulianists’ sacraments are being recognized: not their ordinations, not even their Baptisms. This is true of men and women, the laity and the would-be clerics. But the converting clergy will be permitted to be ordained , provided that they’re found blameless and without reproach. Then the second half says:“Concerning the Paulianists who have flown for refuge to the Catholic Church, it has been decreed that they must by all means be rebaptized; and if any of them who in past time have been numbered among their clergy should be found blameless and without reproach, let them be rebaptized and ordained by the Bishop of the Catholic Church; but if the examination should discover them to be unfit, they ought to be deposed.”
Now, to me, that's also clear. Of all of the Paulianists (men and women, lay and would-be clerics), Nicea points to the deaconesses, and says that they're “to be numbered only among the laity.” Three points to be made here, that I think show why the interpretation suggested in the comments doesn't hold up:“Likewise in the case of their deaconesses, and generally in the case of those who have been enrolled among their clergy, let the same form be observed. And we mean by deaconesses such as have assumed the habit, but who, since they have no imposition of hands, are to be numbered only among the laity.”
- If deaconesses were permitted, why not allow them to be rebaptized and ordained, like their male counterparts? Why number these women among the laity, instead of just ordaining them to the diaconate correctly, as was done with their male counterparts?
- This interpretation make Canon 19 bizarrely redundant. You would have to conclude that the Canon says that (a) none of the ordinations of any of the Paulianists are valid, and then (b) none of the ordinations of any of the Paulianist women are valid. The second part would add nothing that wasn't already the logical conclusion of the first part. If the Paulianist ordinations are invalid, then obviously, the ordinations of Paulianist women are invalid.
- This interpretation would mean that the Canon wasn't just redundant, but outright misleading. Why single out the deaconesses and say that they should be “numbered only among the laity,” if what you really mean is that all of the Paulianist clergy are numbered among the laity?
I'm reminded of the debate of Anglican women's ordination. Catholics reject the validity of Anglican ordinations, and the validity of women's ordination. So if there were a canon addressing mass Anglican conversions to Catholicism, we'd expect it to (a) deal with the problem of how to ordain / re-ordain Anglican clergy generally, and (b) deal with the distinct problem of Anglican women claiming ordination.
In other words, Canon 19 is exactly what we'd expect if Nicea rejected both Paulianist and women's ordinations. But it doesn't make a whole lot of sense if women's ordination to the diaconate was permissible. That's why I don't think that the interpretation suggested in the comments holds up to careful scrutiny.
Update: Womenpriests' analysis of this Canon is worse than I'd realized. They argue that the last part of Canon 19 exists because:
The Council Fathers suddenly realised that the general rule prescribed in (d) makes no sense for Paulianist deaconesses, because in their sect deaconesses were not ordained.This ignores all of the problems outlined above (no one in their sect was validly ordained), but it also introduces the idea that the Council of Nicea made a mistake, suddenly realized it, and just kept going.