I may not know what a co-type is, but...

>What is a cotype? Is it a topotype?

a TOPOTYPE is any specimen that comes from the Type Locality for its species.

If memory serves correctly,
the actual (peculiar) wording is that a topotype is a specimen
originating from the same place where the type was found:
but,as you know, type localities are often
specified/changed/broadened/narrowed/guessed-at
well after the Type was found.
A good example might be Conus cedonulli, L.1767
whose type locality was first designated, I believe, by Danker Vink in the
1980's
as being St.Vincent,West Indies...  -  two hundred years later!

I could be wrong about the above: corrections welcome.
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Does anyone know...   What IS a co-type??
(apart from being an out-of-use term, that is!)

I seem to recall that a co-type was something on the order of a Paratype..
i.e. (similar?) shells from the same Type Locality,
accompanying the Type at time of description,
included in that description and its illustrations.

Again, corrections welcome.


There are many    -type  specifications.
Somewhere, I have a book outlining the lot of them.
Perhaps some brilliant mind out there, familiar with his/her literature,
might illuminate us?