66. Medial groups may be conveniently classified as follows:--A.
_Double Consonants_ (1); B. _Groups of Dissimilar Consonants_: groups
ending in l (2), groups ending in r (3), groups ending in w (4), groups
ending in y (5), groups beginning with l, m, n, r, or s and not
ending in l, r, w, or y (6), all other groups (7). This order will be
followed.[57]
1. It should be noted that the prefixes _ad-_, _sub-_
regularly assimilate their d or b to the following consonant:
✱_ad-rīpāre_ ＞ _arribar_, _sub-venīre_ ＞ _sovenir_. _Sosrire_,
_sosterrar_, _sostraire_ show a substitution of prefix, due, no
doubt, to the analogy of _sospirar_, _sostener_.