What was the difference between Ratramnus's view of the Eucharist and that of Calvin? In the First Eucharistic Controversy (ninth century), Paschasius Radbertus wrote a monograph arguing that the elements in communion were nothing less than the physical flesh and blood of Jesus.  He was widely opposed, and another theologian, Ratramnus, replied.  Everett Ferguson (Church History, I, 18.IV.D) summarizes his view:


  Ratramnus opposed the realistic interpretation of the bread and wine, saying that the body and blood of Jesus Christ are present in a figure, not literally.  The spiritual presence of the body of Christ is a mystery, available only to faith.


This sounds very much like the "spiritual presence" view of the Lord's supper, advocated by John Calvin and widely held today in Reformed theology.

Based on the writings of these two theologians, what are the major similarities and differences regarding their views on the nature of the elements in the Eucharist?
Ligonier Ministries has an article about this question posted on its website, addressing the Eucharistic controversy in which Ratramnus took part and discussing its relationship with Protestantism. The most relevant section:


  The views of Ratramnus are somewhat more difficult to pin down than
  those of Radbertus. He does not advocate a simple symbolic
  memorialism, as Zwingli would do centuries later. Nor does he advocate
  anything like the later Lutheran doctrine. If anything, there are some
  similarities between the views of Ratramnus and the views John Calvin
  would later teach, but even here we must be cautious because there are
  also significant differences. Calvin, for example, would agree with
  Ratramnus when he asserts that we partake of bread and wine with the
  mouth and the body and blood of Christ by faith. But Calvin would say
  that we partake in a spiritual manner of the true body and blood of
  Christ — not what Ratramnus refers to as “spiritual flesh.”