Answer
Plural to singular:
pleurae - pleura
gyri - gyrus
ganglia - ganglium
fissures - fissure
Singular to plural:
villus - villi
tibia - tibiae
encephalitis - encephalitides
cervix - cervices
stoma - stomae
Work Step by Step
Table 1.1 on p. 20 "Singular and Plural Forms of Some Noun
Terminals"