Hello, Grieux.

What you are quoting is from a translation of Justin’s First Apology.
There is a similar translation of the whole text that you can read here:-
http://www.ccel.org/ccel/schaff/anf01.viii.ii.html
(Click on the icon at top-left to bring up the Table of Contents)

The following chapters are particularly relevant to your enquiry:-
Chapter LXV (Administration of the sacraments.)
Chapter LXVI (Of the Eucharist.)
Chapter LXVII (Weekly worship of the Christians.)

To see these in a proper perspective it is advisable to read the whole of the Apology, as well as the introductory note at:- http://www.ccel.org/ccel/schaff/anf01.viii.i.html

As you can see from Chapter I (Address), Justin was writing to the pagan Emperor Antoninus Pius.  Justin’s purpose was to explain to the head of state that the Christian religion did not represent a threat to the Roman Empire.  Whilst the Apology provides some evidence of liturgical practice at the time, it should not be read as if it was complete in that respect, or that it was meant to be used as a rubrical text for the instruction of the Church.

I understand (although I don’t have supporting evidence to hand) that Justin (who wrote in Greek) did, in fact, use a term meaning “president” rather than one meaning “priest”.  But he had a very good reason for doing so.  It would have been counter-productive to his purpose to have used the term “priest” when the Emperor would have understood it to refer to a rival of the pagan priests who were in his favour.  

One thing is for certain, Justin was not writing an apology for the Novus Ordo Missae, and its accompanying Institutio Generalis Missalis Romani.

Nevertheless, his use of the term “president” provided a convenient pretext for the liturgical revolutionaries of the 20th century, in effect, to use it in place of the term “priest”, especially when they defined the Novus Ordo Missae as something quite different from the true Mass that has been handed down to us.

As to the “New Catechism” (Catechism of the Catholic Church), since it promotes the heresies of Vatican II, you would be better off with an approved catechism written before 1960.  None has higher authority that the Roman Catechism (sometimes known as The Catechism of the Council of Trent) promulgated by Pope St Pius V in 1566.  There is an English translation of it here:-
http://www.catholicprimer.org/trent/catechism_of_trent.pdf

I hope you find these remarks of help.