I can't remember when (if) we discussed the only known
laterally-recorded cylinder, ca. 1904.
But I have just added a 4-page article (from 2006) on the sole surviving
example, by one James Wright Van Meter (now buried in LA). A portion of
the celluloid record can be accessed by clicking on the yellow phonograph
admission ticket at the bottom right of the webpage, and the accompanying pdf
article by clicking on its title. The inventor actually discusses his new
zig-zag process on the unbreakable cylinder itself!
Articles like this appear from time to time in CAPS (the Calif newsletter
magazine). The current issue (Dec) will cover, among other things, an
unknown Berliner disc from 1896.