... that "a regular verb of the first conjugation with a sequence of principal parts ending in -are, -avi, -atum
However it would appear that csun website,http://www.csun.edu/~hcfll004/prparts2.html
begs to differ, what with the fourth principal part being -atus
for those same verbs that were listed as "regular" in the Latin-English vocabulary list in the back of Wheelock's. I've checked other web sites. Some say the 4th is -atum, ...