I highly recommend the Catechism on Modernism by Pascendi's ghostwriter Fr. Jean Baptiste Lemius.

I concur 100%.   From personal experience, I had tried to understand
Pascendi by reading it and using a dictionary, and it wasn't enough.  
But I knew I was onto something big.  Then I found "" by Fr. Lemius (reprint by TAN Books) at Catholic Treasures
in Monrovia (now online only), and couldn't wait to "dig in."  Studying
that one little orange book taught me not only what Pascendi is all
about, but what real catechisms in general should be.  It is a most
excellent work, and I can't praise it highly enough.


Apparently there are two titles afoot, but they seem to be the
same book.  Maybe TAN changed the title to "A CATECHISM
OF MODERNISM" when they did the reprint in 1992, for some
reason?  That link above to the read-online/download PDF is really
great, but I highly recommend getting a HARD COPY because you are
going to want to feel the pages in your fingers with this monumental
work.. It's the REAL McCOY!  This link I provided above to Amazon has
it for $4.50.   You can't go wrong.  Log in to Amazon using Matthew's
link here on CI so he gets credit!  


As for Fr. Lemius being the "ghostwriter" for Pascendi, it seems to me
that's perhaps at least partially true, but I have it on good authority
that Cardinal Merry del Val was the principal writer, although he may
have had assistance.  Recall as well that del Val was the author of
the Prayer for true Humility, so it's not too hard to know that he could
have authored Pascendi and never took credit for the work.