"I wonder if this little difference of spelling was a valid reason to consider Cephallepis preoccupied by Cephalepis"
I do not think now but it is one letter difference and so was considered preoccupied in 1897??
One-letter difference rule = [
Art. 56.2] of current ICZN. The rule was introduced at the Copenhagen Congress of Zoology of 1953 (decision, published 1957: [
here]).
In 1945, the rules that were used were those that were introduced in Opinion 147 (1943) [
here]: assuming the same origin and meaning, names differing only in the use of a single vs. double consonnant were to be regarded homonyms; thus the nomenclature in the Peters' Check-list was still 'right'. But it's not any more; in principle,
Cephallepis should have been reinstated after Copenhagen. (Which it was not, obviously.)
If this is Loddiges 1831:
https://www.biodiversitylibrary.org/item/46215#page/26/mode/1up .
Cephallepis is not really published.
This is it. And it's enough to make
Cephallepis available. The name appears in a publication, and it has two available specific names unambiguously placed under it (
T. lalandei (=
lalandi) Vieillot and
T. loddigesii Gould), which qualifies as an indication under [
Art. 12.2.5]. The originally included nominal species are the nominal species denoted by these two names; the type is the first one,
T. lalandi Vieillot, by subsequent designation of Gray 1855 (who spelled it
delalandii). The author of the name is Loddiges under [
Art. 50.2].
The name has been used as valid during the 20th C, albeit very rarely (example from 1902: [
here]), thus it cannot be dealt with by a reversal of precedence under [
Art. 23.9]. It must either be reinstated, or be submitted for suppression to the Commission.