Detailed historical listing of Gaelic typefaces by Michael Everson. He says that it is not always easy to classify Gaelic typefaces. His classification proposal:

First order classification
• Gaelic fonts have Insular letterforms: delta-form d; s-form g; dotless i; round t with no ascender above the crossbar.
• Pseudo-Gaelic fonts may be identical to Gaelic ones in other respects, but are inauthentic in that they have Carolingian letterforms: a bowled g and/or either a round t with its ascender piercing the crossbar or a rectilinear T. May have a tall f or a two-stroke vertical b and d. May have a dotted i (this is a cardinal sin).
• Roman fonts use unmodified Roman forms, but have dots above and acute accents required for Irish Gaelic. If dotted i is used, its dot and the dot of lenition must be harmonized with regard to height.
• Hybrid fonts use both Roman letterforms and Gaelic letterforms. The earliest faces mix special Gaelic glyphs with existing Roman ones. A few faces give Roman capital letters with Gaelic small letters; even if the strokes of the capital letters are "gaelicized", if they are not strictly speaking Gaelic, Hybrid is used to classify the face.
Second order classification
• Manuscript fonts are generally spiky or angular; often irregular.
• Transitional fonts are designs intermediate between faces that reproduce calligraphic manuscript hands and rectified, regularized typographical faces.
• Modern fonts are regularized typographically.
Third order classification
• Angular fonts have the inverted-v type a, though sometimes this contrasts with round-humped h, m, n.
• Round fonts have the script type a.
• Uncial fonts give a strong suggestion of pen-based strokes. Sometimes it is hard to tell the difference between Manuscript and Uncial but the latter is a "pre-Gaelic" class (there are non-Insular Uncials)
• Monowidth fonts are typewriter typefaces.
• Sans-serif fonts have no serifs.
• Grotesque fonts have no serifs.

EXTERNAL LINKS
Gaelic Typefaces: History and Classification
Google search page

INTERNAL LINKS
History of type ⦿ Celtic/Gaelic fonts ⦿ Type in Ireland ⦿ Carolingian typefaces ⦿ Uncial typefaces ⦿

Luc Devroye ⦿ School of Computer Science ⦿ McGill University Montreal, Canada H3A 2K6 ⦿ lucdevroye@gmail.com ⦿ http://luc.devroye.org ⦿ http://luc.devroye.org/fonts.html